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| 4-channel, 16-bit, continuous time data acquisition adc data sheet adar7251 rev. 0 document feedback information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. specifications subject to change without notice. no license is granted by implication or otherwise under any patent or patent rights of analog devices. trademarks and registered trademarks are the property of their respective owners. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781.329.4700 ?2014 analog devices, inc. all rights reserved. technical support www.analog.com features low noise: 2.4 nv/hz input referred voltage noise at maximum gain setting wide input signal bandwidth: 500 khz at 1.2 msps sample rate, 16-bit resolution additional sample rates supported: 300 ksps, 450 ksps, 600 ksps, 900 ksps, and 1.8 msps 4 differential simultaneous sampling channels no active antialiasing filter required lna and pga with 45 db gain range in 6 db steps selectable equalizer flexible data port supports serial or parallel mode supports fsk mode for fmcw radar systems on-chip 1.5 v reference internal oscillator/pll input: 16 mhz to 54 mhz high speed serial data interface spi control 2 general-purpose inputs/outputs 48-lead lfcsp_ss package temperature range: ?40c to +125c single supply operation of 3.3 v qualified for automotive applications applications automotive lsr systems data acquisition systems general description the adar7251 is a 16-bit, 4-channel, simultaneous sampling analog-to-digital converter (a dc) designed especially for applications such as automotive lsr-fmcw or fsk-fmcw radar systems. each of the four channels contains a low noise amplifier (lna), a programmable gain amplifier (pga), an equalizer, a multibit - adc, and a decimation filter. the front-end circuitry is designed to allow direct connection to an mmic output with few external passive components. the adar7251 eliminates the need for a high order antialiasing filter, driver op amps, and external bipolar supplies. the adar7251 also offers precise channel-to-channel drift matching. the adar7251 features an on-chip phase-locked loop (pll) that allows a range of clock frequencies for flexibility in the system. the conv_start input and data_ready output signals synchronize the adc with an external ramp for applications such as fsk-fmcw radar. the adar7251 supports serial and parallel interfaces at programmable sample rates from 300 ksps to 1.8 msps, as well as easy connections to digital signal processors (dsps) and microcontroller units (mcus) in the system.
adar7251 data sheet rev. 0 | page 2 of 72 table of contents features .............................................................................................. 1 ? applications ....................................................................................... 1 ? general description ......................................................................... 1 ? revision history ............................................................................... 3 ? functional block diagram .............................................................. 4 ? specifications ..................................................................................... 5 ? analog channel ............................................................................ 5 ? digital input/output .................................................................... 6 ? power supply ................................................................................. 7 ? digital filter .................................................................................. 8 ? spi port timing ............................................................................ 8 ? serial/peripheral parallel interface (ppi) port timing............ 8 ? absolute maximum ratings .......................................................... 11 ? thermal resistance .................................................................... 11 ? esd caution ................................................................................ 11 ? pin configuration and function descriptions ........................... 12 ? typical performance characteristics ........................................... 14 ? terminology .................................................................................... 17 ? theory of operation ...................................................................... 18 ? low speed ramp radar analog front end ............................ 18 ? main channel overview ........................................................... 18 ? - modulation and digital filtering ..................................... 18 ? differential input configuration .............................................. 19 ? equalizer (eq) ............................................................................ 19 ? using lna/pga, eq, or the input capacitor ........................ 20 ? reference ..................................................................................... 20 ? auxiliary adc ............................................................................ 20 ? power supply ............................................................................... 21 ? ldo .............................................................................................. 21 ? clock requirements ................................................................... 21 ? crystal oscillator ........................................................................ 21 ? pll ............................................................................................... 21 ? gpio ............................................................................................ 23 ? adc data port ........................................................................... 23 ? pcb layout guidelines .................................................................. 33 ? register summary .......................................................................... 34 ? register details ............................................................................... 37 ? clock control register .............................................................. 37 ? pll denominator register ....................................................... 37 ? pll numerator register ............................................................ 37 ? pll control register ................................................................. 38 ? pll status register ..................................................................... 38 ? master enable switch register ................................................. 39 ? adc enable register ................................................................. 39 ? power enable register ............................................................... 40 ? clear the asil errors register .................................................. 41 ? selects which errors to mask register ................................... 42 ? asil error flag register ........................................................... 43 ? asil error code register ......................................................... 43 ? crc value, bits[7:0] register ................................................... 44 ? crc value register .................................................................... 44 ? start calculating the crc value of the register map content register ........................................................................................ 45 ? register map crc calculation done register ...................... 45 ? register map crc value, bits[7:0] register ........................... 45 ? register map crc value, bits[15:8] register ......................... 46 ? low noise amplifier gain control register .......................... 46 ? programmable gain amplifier gain control register ......... 47 ? signal path for adc 1 through adc 4 register .................. 48 ? decimator rate control register ............................................. 49 ? high pass filter control register ............................................. 50 ? daq mode control register .................................................... 51 ? decimator truncate control register ..................................... 52 ? serial output port control register ........................................ 52 ? parallel port control register ................................................... 53 ? adc digital output mode register ........................................ 54 ? auxiliary adc read value registers ...................................... 54 ? auxiliary adc sample rate selection register ..................... 55 ? auxiliary adc mode register ................................................. 56 ? mpx pin modes registers ......................................................... 56 ? mp write value registers .......................................................... 58 ? mp read value registers........................................................... 58 ? spi_clk pin drive strength and slew rate register ........... 59 ? spi_miso pin drive strength and slew rate register ......... 60 ? spi_ss pin drive strength and slew rate register ............... 60 ? spi_mosi pin drive strength and slew rate register ......... 61 ? addr15 pin drive strength and slew rate register ........... 62 ? fault pin drive strength and slew rate register ............... 62 ? fs_adc pin drive strength and slew rate register ............ 63 ? conv_start pin drive strength and slew rate register ..... 64 ? data sheet adar7251 rev. 0 | page 3 of 72 sclk_adc pin drive strength and slew rate register ....... 64 ? adc_doutx pins drive strength and slew rate registers .... 65 ? data_ready pin drive strength and slew rate register ...... 68 ? xtal enable and drive register .............................................. 68 ? adc test register ....................................................................... 69 ? digital filter sync enable register ........................................... 70 ? crc enable/disable register .................................................... 70 ? typical application circuit ............................................................ 71 ? outline dimensions ........................................................................ 72 ? ordering guide ........................................................................... 72 ? automotive products .................................................................. 72 ? revision history 11/14revision 0: initial version adar7251 data sheet rev. 0 | page 4 of 72 functional block diagram adar7251 ch1 - ? adc digital filter auxin1 aux adc iovdd1 , iovdd2 oscillator reference voltage regulator spi control xout xin/mclkin digital interface decimators adc mux ain1p ain1n ain2p ain2n ain3p ain3n ain4p ain4n auxin2 regout_digital avdd1 , avdd2 , avdd3 pllvdd adc_dout0 adc_dout1 adc_dout2/gpio1 adc_dout3/gpio2 adc_dout4 adc_dout5 addr15/adc_dout6 fs_adc/adc_dout7 sclk_adc conv_start data_ready spi_miso spi_mosi spi_clk spi_ss reset , pwdn 12357-001 pllfilt cm avdd avdd dvdd reset por dvdd1 , dvdd2 pllgnd dgnd1, dgnd2, dgnd3 agnd1, agnd2 bias generator pllvdd pll pllvdd fault avdd avdd dvdd lna pga eq biasn biasp ch2 - ? adc digital filter lna pga eq ch3 - ? adc digital filter lna pga eq ch4 - ? adc digital filter lna pga eq figure 1. data sheet adar7251 rev. 0 | page 5 of 72 specifications analog channel avddx = 3.3 v, dvddx = 1.8 v, iovddx = 3.3 v, v ref = 1.5 v internal/external reference, f sample = 1.2 msps, t amb = ?40c to +125c, unless otherwise noted. table 1. parameter test conditions/comments min typ max unit dynamic performance input referred noise spec tral density frequency = 100 hz gain = 9 db 44.7 nv/hz gain = 15 db 23.6 nv/hz gain = 21 db 15 nv/hz gain = 27 db 12 nv/hz gain = 33 db 11.3 nv/hz gain = 39 db 10.9 nv/hz gain = 45 db 10.8 nv/hz frequency = 1 khz gain = 9 db 16 nv/hz gain = 15 db 8.7 nv/hz gain = 21 db 5.4 nv/hz gain = 27 db 4.3 nv/hz gain = 33 db 4 nv/hz gain = 39 db 3.86 nv/hz gain = 45 db 3.83 nv/hz frequency = 100 khz gain = 9 db 9.7 nv/hz gain = 15 db 5.2 nv/hz gain = 21 db 3.3 nv/hz gain = 27 db 2.67 nv/hz gain = 33 db 2.5 nv/hz gain = 39 db 2.44 nv/hz gain = 45 db 2.4 nv/hz equalizer corner frequency setting 1 eq00 54 khz setting 2 eq01 45 khz setting 3 eq10 37 khz setting 4 eq11 32 khz signal to noise ratio (snr) no input signal and reference to 0 dbfs 88 94 db spurious-free dynamic range (sfdr) at ?3 dbfs input, 100 khz 68 82 db total harmonic distortion plus noise (thd + n) at ?3 dbfs input, 100 khz ?80 ?66 db at ?1 dbfs input, 100 khz ?77 ?62 db channel to channel crosstalk at 50 khz, ?3 dbfs input ?94 ?89 db interchannel gain mismatch ?0.5 0 +0.5 db interchannel phase mismatch 0.04 degrees dc offset ?72 dbfs power supply rejection ripple = 100 mv rms on avddx at 1 khz 65 db adar7251 data sheet rev. 0 | page 6 of 72 parameter test conditions/comments min typ max unit analog input full-scale differential voltage gain = 0 db (lna and pga bypass) 5.6 v p-p gain = 9 db 1.987 v p-p gain = 15 db 0.995 v p-p gain = 21 db 0.498 v p-p gain = 27 db 249 mv p-p gain = 33 db 124 mv p-p gain = 39 db 62 mv p-p gain = 45 db 31 mv p-p common-mode rejection ratio (cmrr) at 1 khz 68 db gain error ?0.8 +0.8 db input resistance single-ended 2860 differential 5720 voltage reference in/out (v ref ) at the cm pin 1.5 v conversion sample rate sample rate 0.3 1.2 1.8 msps input signal bandwidth 150 600 900 khz pll input frequency 16 54 mhz output frequency (internal) 115.2 mhz lock time 1 ms ldo regout_digital output voltage used for internal digital core only 1.8 v line regulation avddx as an input 2.97 3.3 3.63 v load regulation used for internal digital core only 1 % auxiliary adc full-scale input 3.3 v p-p sample rate 112.5 450 khz resolution 8 bits inl 0.5 lsb dnl 1 lsb input resistance 1 switched capacitor input at a switching frequency of 112.5 khz 1.2 m 1 from simulation. digital input/output dvddx = 1.8 v, iovddx = 3.3 v, c load = 22 pf. table 2. parameter symbol test conditions/comments min typ max unit input voltage high level v ih 0.7 iovddx v low level v il 0.3 iovddx v output voltage high level v oh i oh = 1 ma iovddx ? 0.60 v low level v ol i ol = 1 ma 0.4 v input capacitance 5 pf input leakage current 10 a data sheet adar7251 rev. 0 | page 7 of 72 power supply avddx = 3.3 v, dvddx = 1.8 v, iovddx = 3.3 v, f s = 1.2 mhz (master mode), pll enabled with 19.2 mhz master clock input, ?3 dbfs, 100 khz input on all channels, unless otherwise noted. table 3. parameter test conditions/comments min typ max unit dvdd on-chip ldo 1.62 1.8 1.98 v current normal operation dvddx external at f s = 1.2 mhz 32 ma power-down standby without master clock 80 a avdd 2.97 3.3 3.6 v current normal operation 4-channel adc, dvddx internal, f s = 1.2 mhz 115 ma power save mode 87 ma power-down reset/pwdn pin held low without master clock 1.1 ma reset/pwdn pin held low with master clock 1.1 ma iovdd 2.97 3.3 3.6 v current input master clock = 19.2 mhz normal operation 4-channel adc; serial mode, 2 channels per data line f s = 1.2 mhz 4 ma f s = 900 khz 3.4 ma f s = 600 khz 2.7 ma f s = 300 khz 2 ma 4-channel adc; parallel mode, byte wide format f s = 1.8 mhz 2.8 ma f s = 1.2 mhz 2.3 ma f s = 900 khz 2 ma f s = 600 khz 1.7 ma f s = 300 khz 1.3 ma power-down reset/pwdn pin held low without master clock 335 a reset/pwdn pin held low with master clock 360 a power dissipation normal operation input master clock = 19.2 mhz dvddx internal, 4-channel adc at f s = 1.2 mhz 400 mw dvddx external, 4-channel adc at f s = 1.2 mhz 294 mw power-down, all supplies reset/pwdn pin held low with master clock 5 mw adar7251 data sheet rev. 0 | page 8 of 72 digital filter table 4. parameter mode factor min typ max unit adc decimation filter at f s =1.2 mhz, decimation ratio = 48 at f s = 1.2 mhz, decimation ratio = 48 pass band ?0.1 db corner 0.166 f s 200 khz pass-band droop at 600 khz ?1.4 db stop band 0.666 f s 800 khz stop-band attenuation 70 db group delay 95 s high-pass filter corner frequency ?3 db, programmable in eight steps 0.729 93.3 hz attenuation see figure 24 in the typical performance characteristics section spi port timing dvddx = 1.8 v, iovddx = 3.3 v, c load = 22 pf, i out = 1 ma. table 5. limit at parameter description min typ max unit spi port see figure 2 t ccph spi_sclk high 50 ns t ccpl spi_sclk low 50 ns f spi_clk spi_sclk frequency 10 mhz t cds spi_mosi setup to spi_sclk rising 10 ns t cdh spi_mosi hold from spi_sclk rising 10 ns t cls spi_ss setup to spi_sclk rising 10 ns t clh spi_ss hold from spi_sclk rising 40 ns t clph spi_ss high 10 ns t cdh spi_miso hold from spi_sclk rising 30 ns t cod spi_miso delay from spi_sclk falling 30 ns t cots spi_miso tristate from spi_ss rising 30 ns serial/peripheral parallel inte rface (ppi) port timing dvddx = 1.8 v, iovddx = 3.3 v, c load = 22 pf, i out = 1 ma. table 6. limit at parameter description min typ max unit input master clock (mclkin) duty cycle mclkin duty cycle; mclkin at 256 f s , 384 f s , 512 f s , and 768 f s 40 60 % f mclkin mclkin frequency, pll in mclk mode 16 54 mhz reset reset pulse, t reset reset/pwdn held low 15 ns pll lock time 1 ms data sheet adar7251 rev. 0 | page 9 of 72 limit at parameter description min typ max unit adc serial port master mode see figure 3 t sckh sclk_adc high, slave mode 10 ns t sckl sclk_adc low, slave mode 10 ns t ds adc_doutx setup to sclk_adc rising, slave mode 10 ns t dh adc_doutx hold from sclk_adc rising, slave mode 5 ns t dd adc_doutx delay from sclk_adc falling 18 ns t fsh fs_adc hold from sclk_adc rising 18 ns t fss fs_adc setup from sclk_adc falling 1 ns adc serial port slave mode see figure 4 t sckh sclk_adc high, slave mode 7 ns t sckl sclk_adc low, slave mode 7 ns t ds adc_doutx valid to sclk_adc rising, slave mode 11 ns t dh adc_doutx hold from sclk_adc rising, slave mode 11 ns t dd adc_doutx delay from sclk_adc falling 2 ns t fsh fs_adc hold from sclk_adc rising 1 ns t fss fs_adc setup from sclk_adc falling 1 ns parallel mode, byte wide format see figure 5; if usingconv_start , see figure 6 for the conv_start to data_ready timing relation t sckh sclk_adc high, master mode 28 ns t sckl sclk_adc low, master mode 28 ns t ds adc_doutx setup to sclk_adc rising, master mode 7 ns t dh adc_doutx hold from sclk_adc rising, master mode 5 ns t dd adc_doutx delay from sclk_adc falling for left justified (lj) mode 6 ns for i 2 s mode, add one sclk_adc period to the t dd of lj mode t csdr conv_start falling to data_ready rising 1.215 s data acquisition (daq) mode conv_start falling to data_ready rising, see figure 6 t drh conv_start rising to data_ready falling 0.44 s t csdr daq16 mode (16 acquisition clock cycles) 1.215 s daq24 mode (24 acquisition clock cycles) 1.8 s daq32 mode (32 acquisition clock cycles) 2.43 s timing diagrams spi_ss spi_sclk spi_mosi spi_miso t cls t cds t cdh t cod t ccph t ccpl t clh t clph t cdh t cots 12357-002 figure 2. spi port timing adar7251 data sheet rev. 0 | page 10 of 72 sclk_adc fs_adc adc_doutx left justified mode adc_doutx i 2 s mode 16-bit clocks per channel (16-bit data) t sckl t dd t dd t sckh t fss t fsh t ds t ds t dh t dh msb msb msb ? 1 12357-004 figure 3. serial port timing master mode sclk_adc fs_adc adc_doutx left justified mode adc_doutx i 2 s mode 16-bit clocks per channel (16-bit data) t sckl t dd t dd t sckh t fss t fsh t ds t ds t dh t dh msb msb msb ? 1 12357-003 figure 4. serial output port timing slave mode t sckh t dh t sckl t ds t dd t dd data_ready sclk_adc lj: adc_doutx i 2 s: adc_doutx msb msb 12357-005 figure 5. ppi timing master mode conv_start data_ready t csdr t drh 12357-006 figure 6. conv_start to data_ready timing data sheet adar7251 rev. 0 | page 11 of 72 absolute maximum ratings table 7. parameter rating avddx to agndx, dgndx ?0.3 v to +3.63 v dvddx to agndx, dgndx ?0.3 v to +1.98 v iovddx to agndx, dgndx ?0.3 v to +3.63 v agndx to dgndx ?0.3 v to +0.3 v analog input voltage to agndx ?0.3 v to +3.63 v digital input voltage to dgndx ?0.3 v to +3.63 v digital output voltage to dgndx ?0.3 v to +3.63 v input current to any pin except supplies 10 ma operating temperature range (ambient) ?40c to +125c junction temperature range ?40c to + 150c storage temperature range ?65c to +150c rohs-compliant temperature soldering reflow 260c stresses at or above those listed under absolute maximum ratings may cause permanent damage to the product. this is a stress rating only; functional operation of the product at these or any other conditions above those indicated in the operational section of this specification is not implied. operation beyond the maximum operating conditions for extended periods may affect product reliability. thermal resistance ja represents junction-to-ambient thermal resistance, and jc represents the junction-to-case thermal resistance. all characteristics are for a standard jedec board per jesd51. table 8. thermal resistance package type ja 1 jc 1 unit 48-lead lfcsp_ss 25 1 c/w 1 jedec 2s2p standard board. esd caution adar7251 data sheet rev. 0 | page 12 of 72 pin configuration and fu nction descriptions 1 2 3 dgnd3 conv_start sclk_adc 4 fs_adc/adc_dout7 5 addr15/adc_dout6 6 adc_dout5 7 adc_dout4 2 4 d v d d 2 2 3 d g n d 2 2 2 d a t a _ r e a d y 2 1 d v d d 1 2 0 d g n d 1 1 9 r e g o u t _ d i g i t a l 1 8 a v d d 2 1 7 x o u t 1 6 x i n / m c l k i n 1 5 p l l v d d 1 4 p l l f i l t 1 3 p l l g n d 4 4 a i n 1 p 4 5 a i n 1 n 4 6 a i n 2 p 4 7 a i n 2 n 4 8 a v d d 3 4 3 r e s e t / p w d n 4 2 f a u l t 4 1 s p i _ s s 4 0 s p i _ c l k 3 9 s p i _ m o s i 3 8 s p i _ m i s o 3 7 i o v d d 2 top view (not to scale) adar7251 25 avdd1 26 biasp 27 biasn 28 agnd2 29 cm 30 auxin2 31 auxin1 32 ain4n 33 ain4p 34 ain3n 35 ain3p 36 agnd1 notes 1. the exposed pad on the bottom of the package must be soldered to the ground plane on the board for power dissipation. 8 adc_dout3/gpio2 9 adc_dout2/gpio1 10 adc_dout1 11 adc_dout0 12 iovdd1 12357-007 figure 7. pin configuration table 9. pin function descriptions pin no. mnemonic type 1 description epad exposed pad. the exposed pad on the bottom of the package must be soldered to the ground plane on the board for power dissipation. 1 agnd1 2 pwr analog ground. this pin is the ground re ference point for all analog blocks in the adar7251 . 2 ain3p ain noninverting input to differential analog channel 3. 3 ain3n ain inverting input to differential analog channel 3. 4 ain4p ain noninverting input to differential analog channel 4. 5 ain4n ain inverting input to differential analog channel 4. 6 auxin1 ain auxiliary adc analog input 1. single-ended analog input channel. 7 auxin2 ain auxiliary adc analog input 2. single-ended analog input channel. 8 cm aio adc reference output. connect a 10 f capacitor in parallel with a 100 nf capacitor from this pin to agndx. 9 agnd2 2 pwr analog ground. this pin is the ground re ference point for all analog blocks in the adar7251 . 10 biasn aout internal bias generator. deco uple to agndx using a 0.47 f capacitor. 11 biasp aout internal bias generator. deco uple to avddx using a 0.47 f capacitor. 12 avdd1 pwr analog supply voltage, 3.3 v. deco uple this supply pin to agndx. see figure 60. 13 pllgnd pwr analog ground for pll. connect to a ground plane directly on the board. 14 pllfilt ain filter components connection for pll. see figure 60. 15 pllvdd pwr analog supply for analog pll, 3.3 v. deco uple to the pllgnd pin (pin13) using a 0.1 f multilayer ceramic capacitor (mlcc). connect to avddx or an external 3.3 v source. it is recommended to add the filter for a clean 3.3 v source and for good pll performance. 16 xin/mclkin ain internal oscillator input/clock input. if using an external crystal, connect it between the xin and xout pins. if not using a crystal, a single-ended clock must be provided at the mclkin pin. the adar7251 accepts a clock frequency range of 16 mhz to 54 mhz. 17 xout aout internal oscillator output connection for external crystal. 18 avdd2 pwr analog supply voltage, 3.3 v. deco uple this supply pin to agndx. see figure 60. 19 regout_digital pwr ldo regulator output for internal digital core (1.8 v, typical). decouple to dgndx. see figure 60. connec t regout_digital to the dvddx pins if using the internal regulator to supplythe 1.8 v to the digital core. 20 dgnd1 3 pwr digital ground. this pin is the ground refe rence point for the digital circuitry on the adar7251 . data sheet adar7251 rev. 0 | page 13 of 72 pin no. mnemonic type 1 description 21 dvdd1 pwr digital core power supply input. connect decoupling capacitors between the dvddx and dgndx pins. see figure 60. the voltage on this pin is 1.8 v. this pin can be connected to regout_digital (pin 19), or to the external 1.8 v source if the internal ldo is not used. 22 data_ready dout adc conversion data ready output. connect to the dsp general-purpose input/output (gpio) in the system. 23 dgnd2 3 pwr digital ground. this pin is the ground re ference point for digital circuitry on the adar7251 . 24 dvdd2 pwr digital core power supply input. connect decoupling capacitors between the dvddx and dgndx pins. see figure 60. the voltage on this pin is 1.8 v. this pin can be connected to regout_digital (pin 19), or to the external 1.8 v source if the internal ldo is not used. 25 iovdd1 pwr logic power supply input. the voltage suppl ied at this pin determines at what voltage the interface operates. connect decoupling capacitors betwee n the iovddx and dgndx pins. see figure 60. 26 adc_dout0 dout adc data output (serial mode) or adc data output bit 0 and bit 8 (ppi mode). refer to the adc serial mode and adc ppi (byte wide mode) se ctions for function information. 27 adc_dout1 dout adc data output (serial mode) or adc data output bit 1/9 (ppi mode). refer to the adc serial mode and adc ppi (byte wide mode) sections for function information. 28 adc_dout2/gpio1 dout adc data output bit 2 and bit 10 (ppi mode)/general-purpose input/output 1. refer to the adc serial mode section for function information. 29 adc_dout3/gpio2 dout adc data output bit 3 and bit 11 (ppi mode)/general-purpose input/ou tput 2. refer to the adc ppi (byte wide mode) section for function information. 30 adc_dout4 dio adc data output bit 4 and bit 12 (ppi mode). refer to the adc ppi (byte wide mode) section for function information. 31 adc_dout5 dio adc data output bit 5 and bit 13 (ppi mode). refer to the adc ppi (byte wide mode) section for function information. 32 addr15/ adc_dout6 dio device address setting for the spi control interf ace/adc data output bit 6 and bit 14 in ppi mode. this pin sets bit 1 of the spi device address. conne ct to either dgndx or iovddx as desired using a 10 k pull-down or pull-up resistor. refer to the adc ppi (byte wide mode) section for function information. 33 fs_adc/ adc_dout7 dio active low frame synchronization signal for defa ult adc data (serial mode)/adc data output bit 7 and bit 15 (ppi mode). refer to the adc ppi (byte wide mode) section for function information. 34 sclk_adc dio serial bit clock for the adc data output (serial mode and ppi mode). this pin is an input in slave mode or is an output in master mode. 35 conv_start din adc conversion start in daq/ppi/serial mode (a ctive low). an active low signal initiates an adc conversion. see the theory of operation section for further details. 36 dgnd3 3 pwr digital ground. this pin is the ground re ference point for digital circuitry on the adar7251 . 37 iovdd2 pwr logic power supply input. the voltage suppl ied at this pin determines at what voltage the interface operates. connect decoupling capacitors betwee n the iovddx and dgndx pins. see figure 60. 38 spi_miso dout spi control interface slave data output. 39 spi_mosi din spi control interface slave data input. 40 spi_clk din spi control interface serial clock input. 41 spi_ss din spi control interface slave select (active low in put). connect an external 10 k pull-up resistor to iovddx. 42 fault dout digital output. this pin becomes active under fault condition. connect an external 10 k pull-up resistor to iovddx. this pin can be used as an interr upt input to the microcontroller or dsp in case of faults. 43 reset/pwdn din active low reset input/power-down. the adar7251 requires an external reset signal to hold the reset input low until avddx is within the specified operating range. wh en held low, this pin places the adar7251 into power-down mode. 44 ain1p ain noninverting input to differential analog channel 1. 45 ain1n ain inverting input to differential analog channel 1. 46 ain2p ain noninverting input to differential analog channel 2. 47 ain2n ain inverting input to differential analog channel 2. 48 avdd3 pwr analog supply voltage. decouple this supply pin to agndx. 1 pwr is power supply or ground pin, ain is analog input, aio is analog input/output, aout is an alog output, din is digital inpu t, dout is digital output, and dio is digital input/output. 2 all the agndx pins (agnd1 and agnd2) are shorted internally and recommended to be connected to a single ground plane on the bo ard. refer to the pcb layout guidelines section for details. 3 all the dgndx pins (dgnd1, dgnd2, and dgnd3) are shorted internally and recommended to be connected to a single ground plane o n the board. refer to the pcb layout guidelines section for details. adar7251 data sheet rev. 0 | page 14 of 72 typical performance characteristics 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 03060 frequency (khz) amplitudef (dbfs) 90 120 150 12357-100 figure 8. fft with ?60 dbfs, 100 khz input at f s = 300 khz 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 04590 frequency (khz) amplitudef (dbfs) 135 180 225 12357-101 figure 9. fft with ?60 dbfs, 100 khz input at f s = 450 khz 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 060120 frequency (khz) amplitudef (dbfs) 180 240 300 12357-102 figure 10. fft with ?60 dbfs, 100 khz input at f s = 600 khz 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 090180 frequency (khz) amplitudef (dbfs) 270 360 450 12357-103 figure 11. fft with ?60 dbfs, 100 khz input at f s = 900 khz 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 0 120 240 frequency (khz) amplitudef (dbfs) 360 480 600 12357-104 figure 12. fft with ?60 dbfs, 100 khz input at f s = 1.2 mhz 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 0 180 360 frequency (khz) amplitudef (dbfs) 540 720 900 12357-105 figure 13. fft with ?60 dbfs, 100 khz input at f s = 1.8 mhz data sheet adar7251 rev. 0 | page 15 of 72 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 076152 frequency (khz) amplitudef (dbfs) 228 304 380 12357-110 figure 14. fft with ?60 dbfs, 100 khz input, daq16, at f s = 758 khz 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 03876 frequency (khz) amplitudef (dbfs) 114 152 190 12357-111 figure 15. fft with ?60 dbfs, 100 khz input, daq24, at f s = 380 khz 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 02040 frequency (khz) amplitudef (dbfs) 60 80 100 12357-109 figure 16. fft with ?60 dbfs, 10 khz input, daq32, at f s = 200 khz 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 02040 frequency (khz) amplitudef (dbfs) 60 80 100 12357-107 figure 17. fft with ?60 dbfs, 10 khz input, daq16, at f s = 200 khz 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 02040 frequency (khz) amplitudef (dbfs) 60 80 100 12357-108 figure 18. fft with ?1 dbfs, 10 khz input, daq16, at f s = 200 khz 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 0 120 240 frequency (khz) amplitudef (dbfs) 360 480 600 12357-106 figure 19. fft with ?1 dbfs, 100 khz input, at f s = 1.2 mhz adar7251 data sheet rev. 0 | page 16 of 72 ? 10 ?15 amplitude (db) ?20 ?25 ?30 ?35 ?40 11 0 frequency (khz) 100 no eq_cap_ctrl eq_cap_ctrl = 00 eq_cap_ctrl = 01 eq_cap_ctrl = 10 eq_cap_ctrl = 11 12357-014 figure 20. eq 0 5 10 15 20 25 30 35 40 45 50 1 10 100 amplitude (db) frequency (khz) lna + pga gain = 45db lna + pga gain = 39db lna + pga gain = 33db lna + pga gain = 27db lna + pga gain = 21db lna + pga gain = 15db lna + pga gain = 9db 12357-015 figure 21. lna + pga gain 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 ?160 ?180 ?200 10m 1m 100k 10k 12357-115 magnitude (db) frequency (hz) figure 22. frequency response, adc digital filter at f s = 1.2 mhz 0 ?0.5 ?1.0 ?1.5 ?2.0 ?2.5 ?3.0 ?3.5 ?4.0 ?4.5 100k 10k 12357-116 frequency (hz) magnitude (db) figure 23. adc digital filter pass band at f s = 1.2 mhz 0 ?5 ?10 ?15 ?20 ?25 100k 10k 1k 10 100 12357-117 magnitude (db) frequency (hz) 93.300hz 46.600hz 23.300hz 11.700hz 5.830hz 2.910hz 1.460hz 0.729hz figure 24. adc high-pass f ilter frequency response data sheet adar7251 rev. 0 | page 17 of 72 terminology integral nonlinearity (inl) inl is the maximum deviation from a straight line passing through the endpoints of the adc transfer function. for the adar7251 , the endpoints of the transfer function are zero scale, a point ? lsb below the first code transition, and full scale, a point ? lsb above the last code transition. differential nonlinearity (dnl) dnl is the difference between the measured and the ideal 1 lsb change between any two adjacent codes in the adc. offset error offset error is the deviation of the first code transition (00000) to (00001) from the ideal (such as ground + 0.5 lsb). gain error for the adar7251 , gain error is the deviation of the last code transition (111110) to (111111) from the ideal (such as v ref C 1.5 lsb) after the offset error is adjusted out. signal-to-noise ratio (snr) snr is the ratio of the rms value of the actual input signal to the rms sum of all other spectral components below the nyquist frequency, excluding harmonics and dc. the value for snr is expressed in decibels (db). total harmonic distortion (thd) thd is the ratio of the rms sum of harmonics to the fundamental. for the adar7251 , thd is defined as ?? 1 2 6 2 5 2 4 2 3 2 2 log20db v vvvvv thd ???? ? where: v 1 is the rms amplitude of the fundamental. v 2 , v 3 , v 4 , v 5 , and v 6 are the rms amplitudes of the second through the sixth harmonics. dynamic range (dnr) thd + n is measured in db with an input level of ?60 dbfs (?60 db relative to the full-scale input). then, 60 db is added to the measured thd + n value and is expressed in decibels. for example, when measuring 36 db thd + n with a ?60 dbfs input, dnr is 60 + 36 = 96 db. peak harmonic or spurious noise peak harmonic or spurious noise is defined as the ratio of the rms value of the next largest component in the adc output spectrum (up to f s /2 and excluding dc) to the rms value of the fundamental. normally, the value of this specification is determined by the largest harmonic in the spectrum, but for adcs where the harmonics are buried in the noise floor, it is a noise peak. adar7251 data sheet rev. 0 | page 18 of 72 theory of operation low speed ramp rada r analog front end the most common application for the adar7251 is low speed ramp, frequency modulated, continuous wave, or frequency shift keying radar (lsr-fmcw or fsk-fmcw). figure 28 shows a typical block diagram of an lsr/fsk radar system for a 4-channel application. the signal chain may require up to eight channels, each including an lna, a pga, and a - adc. all input channels on the adar7251 sample the input signals simultaneously. the adar7251 also delivers secondary features required by an lsr radar system: a 2-channel, auxiliary 8-bit adc and two gpios. main channel overview the adar7251 features an on-chip, fully differential lna and pga to feed the - input pins, as well as a digital filter block to perform the required filtering on the - modulator output. using this - conversion technique with added digital filtering, the analog input converts to an equivalent digital word. the adar7251 uses an internal 1.5 v reference voltage. -? modulation and digital filtering the input waveform applied to the modulator is sampled, and an equivalent digital word is output to the digital filter at a rate equal to the modulator clock. the modulator is clocked by 48 f s (57.6 mhz clock signal, f iclk , for f s =1.2 mhz). by employing oversampling, the quantization noise spreads across a wide bandwidth (see figure 25). this means that the noise energy contained in the bandwidth of interest is reduced. to further reduce the quantization noise, a third-order modulator is employed to shape the noise spectrum so that most of the noise energy is shifted out of the signal band (see figure 26). the digital filtering that follows the modulator removes the large out-of-band quantization noise (see figure 27) while also reducing the data rate at the input of the filter to 1.2 mhz or less at the output of the filter, depending on the decimation rate used. the total channel noise of the adar7251 depends on the bandwidth specification and the selected analog input range. the data rate at the output of the adar7251 can be reduced further to meet specific application requirements. the continuous time modulator removes the need for a high order antialias filter at the input to the adar7251 . the continuous time - modulator used within the adar7251 has inherent antialiasing due to oversampling. the device uses 48 over- sampling. this relaxes the requirement of filtering required at the input of the adc. typically, a single pole passive resistor capacitor (rc) filter is sufficient. quantization noise f iclk /2 band of interest 12357-017 figure 25. - adc, quantization noise f iclk /2 noise shaping band of interest 12357-018 figure 26. - adc, noise shaping f iclk /2 band of interest digital filter cutoff frequency 12357-019 figure 27. - adc, digita l filter cutoff frequency m pa mmic vco antenna ramp generator dsp mcu data port adc lpf hpf can/ flexray psu adar7251 pga lna adc lpf hpf pga lna adc lpf hpf pga lna adc lpf hpf pga lna 12357-016 figure 28. radar system overview data sheet adar7251 rev. 0 | page 19 of 72 differential input configuration the adar7251 main adc input channel consists of an lna, a pga, a continuous time - adc, and internal bias resistors that set the common-mode voltage on the input of the lna. the pga includes an equalizer (eq) function that gains up low amplitude, high frequency signals. typically, in an automotive radar application, the analog inputs of the adar7251 connect directly to the mixer output (see figure 29). if additional external filtering is required, the external c1, c2, and c3 capacitors can be used. these capacitors, together with the r1, r2, and the mixer output impedance, create an external filter that removes dc components and high frequency noise from the adc inputs. - ? adc ainxp ainxn c1 r1 r2 c3 c2 r m r m mixer adar7251 avddx gain + mux mmic output typical one input channel 12357-020 figure 29. typical differential input channel configuration a monolithic microwave integrated circuit (mmic) mixer output impedance, r m , with capacitor c3, forms a single-pole, low-pass filter that reduces high frequency spurs from the adar7251 inputs. two capacitors, c1 and c2, with the adar7251 internal resistance of r1 and r2, produce a high-pass filter that removes dc components from the input signal. each - adc input is preceded by its own lna and pga gain stage. the variable gain settings ensure that the device is able to amplify signals from a variety of sources. the adar7251 offers the flexibility to choose the most appropriate gain setting to utilize the wide dynamic range of the device. the lna stage gain can be set using register 0x100 in 6 db steps. the default gain is 6 db. the pga gain can be set independently using register 0x101and has a default gain of 2.92 db. the total lna + pga gain range is 36 db. the gain settings, along with the adar7251 analog input range and channel noise specifications, are shown in the specifications section (see table 1). the default gain with lna + pga is 9 db (2.8), so that the full-scale differential input signal is 0.7 v rms. however, if a direct path is chosen and lna + pga is bypassed, the full-scale input signal to the adc is 2 v rms differential. high-pass filter (hpf) the external input coupling capacitors form the passive first order, high-pass filter with the input impedance of the adar7251 . this filter can also be used as a passive equalizer to boost the high frequency if desired. the corner frequency can be set to the desired frequency using the equation f 3db = 1/(2 r1 c1) where r1 = r2 (typical) is 2.86 k and c2 = c1 (see figure 29). low-pass filter (lpf) the low-pass filter is formed by adding the capacitor across the differential input pins. the value of the source resistance driving the adc dictates the corner frequency of the filter. use the following equation to set the corner frequency to the desired frequency: f 3db =1/(4 r m c3) where r m (typical) is the source resistance of the mmic output. input routing figure 30 shows the typical 2-channel input block with multiplexers and input signal routing inside the adar7251 . for simplicity, the connections in figure 30 are shown as single- ended, although they are differential. the input signal can be routed through lna + pga, lna + pga + eq, or direct to the adc. register 0x102 is used to select the multiplexer at the input of the adc. the inputs to the adc can be swapped between adjacent channels, for example, channel 1 can be sent to adc2 and the channel 2 input can be sent to adc1. in addition, the auxiliary input 1 and input 2 can be sent directly to the adc. in this case, auxin1 becomes a noninverting input, and auxin2 becomes an inverting input to form a differential pair. the default path is lna + pga + adc. eq mux select 1 input mux 1 ct adc 1 eq input mux 2 ct adc 2 mux select 2 lna + pga 1 lna + pga 2 input 1 input 2 test input (common for all adcs) 12357-021 figure 30. typical 2-channel input block equalizer (eq) the output of lna + pga can be routed to an equalizer block. in lsr-fmcw radar systems, the distance between the radar and the object affects signal amplitude and frequency. distant objects have a higher frequency and smaller amplitude. the eq provides frequency dependent gain to boost these signals. this provides easier detection of distant objects in a system. excellent noise performance relies on an ultralow noise lna at the beginning of the signal chain and a high precision adc architecture. enable the eq path in register 0x102. the eq is a first order, high-pass adar7251 data sheet rev. 0 | page 20 of 72 type. the cutoff frequency can be either 32 khz (default), 37 khz, 45 khz, or 54 khz. select the eq cutoff frequency in eq_cap_ctrl, bits[1:0] in register 0x301 (see figure 20 in the typical performance characteristics section). using lna/pga, eq, or the input capacitor the input passive filter, along with lna + pga and eq, can be used to achieve the desired frequency response in the system. see figure 31, figure 32, and figure 33 for typical examples. figure 31 shows the frequency response plot by varying the input coupling capacitor value, with the lna + pga gain and eq fixed. figure 32 shows the frequency response plot by varying the lna + pga gain, with the input coupling capacitor and eq fixed. figure 33 shows the frequency response plot by varying the eq setting, with the input coupling capacitor and lna + pga gain fixed. ?70 ?65 ?60 ?55 ?50 ?45 ?40 ?35 ?30 ?25 ?20 ?15 ?10 ?5 0 5 10 15 20 25 30 35 40 45 0.1 1 10 100 amplitude (db) 1k 10k 100k 1m frequency (hz) 10f 1f 1nf 10nf 100pf 12357-112 figure 31. frequency response , coupling capacitor change 0.1 1 10 100 amplitude (db) 1k 10k 100k 1m frequency (hz) 12357-113 45db gain 33db gain 27db gain 21db gain 9db gain ?35 ?30 ?25 ?20 ?15 ?10 ?5 10 5 0 15 20 25 30 35 40 45 50 55 60 65 70 figure 32. frequency response, coupling gain change ?75 ?70 ?65 ?60 ?55 ?50 ?45 ?40 ?35 ?30 ?25 ?20 ?15 ?10 ?5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 0.1 1 10 100 amplitude (db) 1k 10k 100k 1m frequency (hz) 33db gain 45db gain 27db gain 21db gain 12357-114 figure 33. frequency response, coupling eq change reference the internal reference of the adar7251 is set to 1.5 v. this 1.5 v reference is available at the cm pin. decouple the cm pin to the agndx pin using a 10 f mlcc in parallel with a 100 nf mlcc. the 1.5 v reference is current-limited and not designed to drive an external load. employ an external buffer circuit if this reference is required for use with external circuits. the internal reference voltage can be overdriven externally if required. auxiliary adc the adar7251 includes a 2-channel, auxiliary successive approximation register (sar) adc for low frequency housekeeping functions in the system. these functions include dc voltage monitoring and temperature monitoring. the auxiliary adc uses avddx as the power supply; therefore, the input range is limited from 0 v to avddx. the adc uses a time multiplexing technique to sample the two auxiliary inputs. the multiplexer in the front of the adc selects the input for the conversion. the sample rate of the adc is selectable between 112.5 khz and 450 khz. the default sample rate is 112.5 khz. when 2-channel operation is selected, the set sample rate is the effective sample rate. if only one channel is selected, the effective sample rate is double the set value. the resolution of the adc is eight bits, and the adc output is straight binary. the adc output is stored in the internal registers, which are read via the spi port. register 0x200 stores the current conversion value for input 1 and input 2. in addition, register 0x201 stores the last sample value. the adc sample rate can be selected using register 0x210, and register 0x211 is used for selecting the input to the adc. by default, the auxinx pins are sampled. if the aux_adc_mode bit (bit 0 of register 0x211) is set to 1, only one input is sampled at twice the sample rate. because the auxiliary adc is not continuous, care must be taken to ensure that the input signals are band limited and time multiplexed to prevent aliases. the auxiliary adc inputs are switched capacitor type; therefore, the input impedance is capacitive during the sampling phase. the typical source impedance must be less than 1 k to ensure that the input settles before the sample value is held internally. the data sheet adar7251 rev. 0 | page 21 of 72 source driving the adc inputs must be able to drive at least 20 pf, excluding the parasitic capacitance on the board. a uxin1 aux adc a uxin2 12357-022 figure 34. auxiliary adc power supply the adar7251 uses three supplies: 3.3 v for avddx, 1.8 v for dvddx, and 3.3 v for iovddx. avddx and iovddx must be supplied to the device, but the supply to the dvddx pins can be either generated by an internal ldo, or provided externally by turning off the ldo. the avddx pins supply the analog core of the adc, and the dvddx pins supply the digital core of the adc. the iovddx pins supply the digital input/output pins of the adar7251 . decouple all power supplies to ground with a 0.1 f and a 10 f x7r mlcc for best adc performance. the device provides the exposed pad underneath, which must be connected to the ground plane with thermal vias. all the ground pins must be connected to the single ground plane on the pcb with the shortest possible path close to the respective pins. ldo the internal ldo generates the dvddx voltage (1.8 v) required for the digital core. the ldo takes the avddx (3.3 v) supply and regulates down to 1.8 v. external decoupling capacitors are required to ensure clean power to the digital core. if using the internal 1.8 v supply for the digital core, the regout_digital pin must be externally connected to the dvddx pins. the 1 nf mlcc, in parallel with 0.1 f and 10 f capacitors, are recom- mended at the dvddx pins to decouple the high frequency noise. clock requirements to achieve the specified dynamic performance, use an external crystal at the xin/mclkin and xout pins. alternatively, provide the single-ended clock at the mclkin input via an mcu/dsp controller. the adar7251 features an internal pll block that accepts the clock frequency in a range of 16 mhz to 54 mhz, via either the clock available in the system, or an external crystal. an external clock must be connected to the xin/ mclkin pin and must be within the 0 v to 3.3 v p-p. crystal oscillator the external quartz crystal can be connected across the xin and xout pins. when using the crystal, use register 0x292 to enable the crystal oscillator block. the output of the crystal oscillator is an input to the pll. the typical supported frequency range is 16 mhz to 54 mhz. select load capacitors c1 and c2 for the crystal based on the recommendation of the crystal manufacturer. determine the value of r1 based on the crystal current rating. adar7251 xin y1 r1 c1 c2 xout 12357-023 figure 35. crystal oscillator pll the pll provides the stable clock for the internal blocks. it uses the clock input at the xin/mclkin pin as a reference to generate the core clock. set the pll for either integer or fractional mode. the pll multipliers and dividers (x, r, m, and n) are programmed using register 0x000 to register 0x003. the pll can accept input frequencies in the range of 16 mhz to 54 mhz, either directly from an external source, or using the crystal connected at the xin/mclkin and xout pins. the pll output frequency is fixed at 115.2 mhz. x adc clock internal pll output 115.2mhz x (r + n m) 2 xin pll 12357-024 figure 36. pll block diagram the pll requires an external loop filter, which is fixed (see figure 37). for temperature sensitive applications, the loop filter components must be appropriate. the pll loop filter capacitors must be npo type for best temperature performance. pllfilt pllgnd 390pf 5.6nf 1k ? 12357-025 figure 37. pll loop filter place the pll loop filter close to the pllfilt pin to prevent crosstalk from other sources on the board. in addition, take care to decouple the pllvdd supply to the pll. it is recommended that x7r mlcc or better dielectric mlccs of 1 nf be added in parallel with 0.1 f and 10 f capacitors close to the pllvdd pin. see the pcb layout guidelines section for details. adar7251 data sheet rev. 0 | page 22 of 72 table 10 describes the registers used to set the pll. table 10. registers used to set the pll register name description 0x000 clk_ctrl uses the pll output for the internal master clock, or bypasses the pll 0x001 pll_den sets the 16-bit denominator of the fractional part (m) 0x002 pll_num sets the 16-bit numerator of the fractional part (n) 0x003 pll_ctrl sets the pll mode, pll enable, 4-bit integer multiplier (r), and 4-bit integer divider (x) 0x005 pll_lock checks the pll lock status the pll can be used in either integer mode or fractional mode. integer mode use integer mode when the input clock frequency is an integer multiple of the pll output frequency, governed by the following equation: f pll = ( r / x ) f in where f pll = 115.2 mhz. for example, if f in = 19.2 mhz, then ( r / x ) = f pll (pll required output )/ f in = 6 therefore, r and x are set as follows: r = 6, and x = 1 (default). to route the clock through the pll, first set register 0x000 to 0x0001. in integer mode, the values set for n and m are ignored; leave register 0x001 and register 0x002 at default. table 11 shows the name, function, and required settings for the bits in register 0x003. table 11. required writes for register 0x0003, integer mode bits name function required setting [15:11] pll_integer_div sets the r value 00110 [7:4] pll_input_prescale sets the x value 0001 1 pll_type sets the integer mode for the pll 0 0 pll_en enables the pll 1 set register 0x003 to 0011000000000001, that is, 0x3011. to check the status of the pll, read register 0x0005. fractional mode fractional mode is used when the available clock input at xin/mclkin is a fractional multiple of the desired pll output; it is governed by the following equation: f pll = f in ( r + ( n / m ))/ x for example, if xin/mclkin = 16 mhz, the pll output is 115.2 mhz. to find the values of r, n, an d m, use the following equation: f pll = f in ( r + ( n / m ))/ x where: f pll = 115.2 mhz. f in = 16 mhz. to find the values of r, n, m, and x, use the following equation: (r + ( n / m ))/ x = 115.2 mhz/16 mhz = 7.2 = 7 + (2/10) therefore, r, x, n and m can be set as follows: r = 7, x = 1 (default), n = 2, and m =10. to route the clock through the pll, first set register 0x000 to 0x0001. see table 12 for the required register settings while in fractional mode. set register 0x003 to 0011100000000001, that is, 0x3813. to check the status of the pll, read register 0x005. pll lock acquisition register 0x005 is a read only register that indicates the pll status. after writing the pll settings, it is recommended to read the pll lock status bit to ensure that the pll is locked. a pll_lock bit value of 1 indicates that the pll is locked. table 12. required register writes for fractional mode register bits name func tion required setting 0x0001 [15:0] pll_den sets the m va lue 0000000000001010 (that is, 0x000a) 0x0002 [15:0] pll_num sets the n va lue 0000000000000010 (that is, 0x0002) 0x0003 [15:11] pll_integer_div sets the r value 00111 [7:4] pll_input_prescale sets the x value 0001 1 pll_type sets the fractional mode for the pll 1 0 pll_en enables the pll 1 data sheet adar7251 rev. 0 | page 23 of 72 gpio the adar7251 contains two gpios: pin 28 and pin 29. these pins are dual function. they serve as adc data output pins in ppi mode, or as gpios in serial mode . these pins can be configured as inputs or outputs, and are read back or programmed via the spi control interface. register 0x250 and register 0x251 are used for setting gpio1 and gpio2, respectively. typical applications for these pins include monitoring the status of logic signals or controlling external devices. use the gpio pins for low speed serial communication. configure the gpio pins by writing to the gpio configuration registers, register 0x250 and register 0x251. note that, in these registers, the gpio pins are referred to as the multipurpose (mpx) pins, each gpio pin has associated bits in the gpio configuration register that define a status of the pin and whether the gpio is used as an input or an output, as well as the debounce period. register 0x260 and register 0x261 can be used to output 1 or 0 to gpio1 and gpio2, respectively. register 0x270 and register 0x271 provide the read value from gpio1 and gpio2, respectively. adc data port the adar7251 digital interface port provides multiple options for accessing the adc data and connecting to dsp or micro- controllers in the system. the digital interface port can be set as serial mode or parallel mode. note that, throughout the remainder of the data sheet, multifunction pins are referred to by the relevant function in text and figures, where applicable. adc serial mode the adc serial port uses the conversion start pin ( conv_start ), the frame sync pin (fs_adc/adc_dout7), the bit clock pin (sclk_adc), and two data output pins (adc_dout0 and adc_dout1). conv_start can be disabled if it is not required in the system. the serial port can be set to either master or slave mode. the adc output data is twos complement, 16-bit binary. depending on the mode setup, the frame sync and bit clock pin directions change. in master mode, the adar7251 generates these signals, whereas in slave mode, these signals are provided by the external dsp. the adc_dout0 and adc_dout1 pins are always set as outputs, independent of the master or slave mode. the data format is fixed to msb first. the serial port is powered using the iovddx supply. take proper care to ensure decoupling of the high frequency noise on this pin to prevent jitter on the clock and data outputs. connect a 100 nf mlcc is recommended to be connected to the iovddx pins as close as possible with direct connection to the dgndx pins and a ground plane on the board. because the bit clock rate is in the 40 mhz range, traces on the board require proper attention. the bit clock and data pin (adc_doutx) must be traced out with transmission line considerations. if the clock is connected to multiple devices, the stubs must be properly terminated to reduce reflections. microstrip or stripline traces are recommended for these pins. increase the drive strength for the digital output pins using register 0x0280 through register 0x292. the adar7251 consists of four adcs. data is available in two pairs on the adc_dout0 and adc_dout1 pins: channel 1 and channel 2 on adc_dout0, and channel3 and channel 4 on adc_dout1 in 2-channel mode. each channel uses 16 bits; for two channels, 32-bit clocks are required. the frame sync signal (fs_adc) sets the sample rate for the adc. therefore, the typical bit clock rate for a sample rate of 1.2 mhz is 32 1.2 mhz = 38.4 mhz adc serial master mode in master mode, the adc generates the bit clock (sclk_adc) and frame sync (fs_adc) signals. the sample rate is restricted to a maximum of 1.2 mhz in serial mode. two pins are provided for the serial data: adc_dout0 and adc_dout1. by default, each pin provides the two channel output. in addition, all four channels can be output from one data pin, adc_dout0. the bit clock rate depends on the sample rate and the number of channels per data pin used. see table 13 for available options. figure 38 shows the typical connections diagram for adc serial master mode table 13. bit clock rate options for adc serial mode number of channels per adc_dout0/adc_dout1 pin fs_adc (mhz) sclk_adc (mhz) 2 0.3 9.6 4 0.3 19.2 2 0.45 14.4 4 0.45 28.8 2 0.6 19.2 4 0.6 38.4 2 0.9 28.8 4 0.9 57.6 2 1.2 38.4 4 1.2 not applicable 2 1.8 57.6 1 4 1.8 not applicable 1 supported in master mode only. adar7251 data sheet rev. 0 | page 24 of 72 sclk_adc/adc_dout7 fs_adc adc_dout0 slave dsp adar7251 master adar7251 master xin/mclkin xout xi/mclkinn xout sport1 sport2 optional for > 4 channels mclkin adc_dout1 sclk_adc/adc_dout7 fs_adc adc_dout0 adc_dout1 oscillator 12357-026 figure 38. typical connection diagram for adc serial master mode figure 41 and figure 42 show the waveforms for the serial modes without the conv_start signal. adc serial master mode with conv_start the adc provides the conv_start signal to synchronize the adc conversion data with an external ramp signal used in a fmcw system. use the cs_override bit (register 0x1c2, bit 1) to enable or disable the conv_start signal. this bit is disabled by default. when the cs_override bit is enabled with adc serial master mode, the serial port waits for the conv_start signal from the external dsp or mcu in the system. the conv_start signal is used to indicate the start of the ramp signal in the system. the conv_start signal is active low and needs an external pull-up resistor to iovddx. when the conv_start signal is high, the adc remains running internally, but the data and clocks are not output from the serial port. therefore, there is no data output to the external dsp while this signal is logic high. when the conv_start signal goes low, indicating the start of the ramp signal, the serial port starts outputting the clocks and data. the external dsp can grab the data on the adc serial port based on the frame sync and serial clock. the data is synchronous to the external ramp signal. the following precautions must be taken into account while using adc serial master mode with conv_start : ? the very first sample data may not be complete and may need to be ignored. this is because the conv_start signal is asynchronous to the internal adc clocks, and may request the data anywhere in the middle of the internal frame sync signal. ? the digital filter sync enable bit in register 0x30e is used to synchronize the internal digital filter to the serial port clocks. this bit is enabled by default, therefore, the digital filter attempts to synchronize to the serial port clocks. in serial master mode, this bit must be disabled by writing 0x0000 to register 0x30e. this is an important step because the digital filter is already synchronized to the internal serial port clocks and does not need to be resynchronized based on the external asynchronous demand of the conv_start signal. see figure 39 for waveforms. on time ramp profile conv_start fs_adc sclk_adc see note 1 notes 1. ignore first and last samples because conv_start is not synchronous to internal adc clock. frequency (ghz) off time 1 frame clock period 32 bit clocks see note 1 12357-133 figure 39. typical timing waveforms for adc serial master mode with conv_start master adar7251 slave dsp xin/mclkin oscillator xout gpio1 gpio2 conv_start data_ready 12357-132 sport1 mclkin sclk_adc fs_adc/dout7 adc_dout0 adc_dout1 figure 40. adc serial master mode with conv_start data sheet adar7251 rev. 0 | page 25 of 72 0 31 15 sclk_adc fs_adc adc_dout0 adc_dout1 channel 2 channel 3 channel 4 channel 1 12357-027 figure 41. serial mode, two channels per the adc_doutx pins 0 sclk_adc fs_adc a dc_dout0 31 15 channel 1 channel 2 channel 3 channel 4 63 12357-028 figure 42. serial mode, 4 channels per the adc_doutx pins sclk_adc fs_adc/adc_dout7 adc_dout0 master dsp master spi adar 7251 slave adar 7251 slave xin/mclkin spi_ss xin/mclkin spi_ss sport1 optional for > 4 channels f clk = 16mhz to 54mhz adc_dout1 sclk_adc fs_adc/adc_dout7 adc_dout0 adc_dout1 spi_sclk spi_sclk spi_mosi spi_mosi spi_miso spi_miso spi_mosi spi_sclk spi_ss1 spi_ss2 mclkout spi_miso 12357-029 figure 43. typical connection diagram for adc serial slave mode adc serial slave figure 43 shows the typical connection diagram for adc serial slave mode. in this mode, the directions of the frame sync and bit clock pins change. both pins are inputs and must be provided with bit clock and frame sync signals via an external dsp. the adc_dout0 and adc_dout1 pins are always used as outputs. the data format is fixed as msb first. the adc must be provided with master clock from the dsp to synchronize the ports. adc ppi (byte wide mode) adc ppi mode is parallel byte wide mode and, in this mode, the device is always master. in this mode, the adc outputs the bit clock and data. provide the adc port with a conversion start signal ( conv_start ) if selected. this initiates the conversion process. when the adc is ready with conversion data, it pulls the data_ready pin high to indicate the data ready status to the dsp. the adc then provides the bit clock, sclk_adc. the data is available on the rising edge of the bit clock. the maximum sample rate supported is 3.6 mhz in this mode. the data is available on the adc_dout0 through adc_dout7 pins, one byte at a time. the adc data is twos complement, 16-bit binary, but the 16-bit data is split into two bytes: a higher byte and a lower byte (each is 8 bits wide). the higher byte is output first, and is followed by the lower byte. the bit clock (sclk_adc) rate depends on the sample rate setting. see table 14 for available options. note that in the ppi mode, the fs_adc output is not adar7251 data sheet rev. 0 | page 26 of 72 available. this mode may be useful if the dsp port cannot support the 38.4 mhz data rate. the data rate is less than that of the serial port; however, it uses more pins for data. table 14. bit clock rate options for adc ppi byte wide mode number of channels fs_adc (mhz) sclk_adc (mhz) data output pins 2 1.2 4.8 adc_dout0 through adc_dout7 4 1.2 9.6 adc_dout0 through adc_dout7 2 1.8 7.2 adc_dout0 through adc_dout7 4 1.8 14.4 adc_dout0 through adc_dout7 the other sample rates supported are 300 khz, 600 khz, 900 khz, 2.4 mhz, and 3.6 mhz. the highest serial clock supported is 57.6 mhz. however, as the sample rate increases beyond 1.2 mhz, the adc resolution decreases. at the highest sample rate of 3.6 mhz, the adc resolution is limited to 11 bits. figure 44 shows the typical connections diagram for adc ppi master mode. figure 45 and figure 46 show waveforms for ppi 2-channel and ppi 4-channel mode. adc_dout0 to adc_dout7 adc_dout0 to adc_dout7 master adar7251 slave dsp xin xout mclkout sclk gpio1 gpio2 conv_start data_ready sclk_adc 12357-030 figure 44. typical connection diagram for adc ppi master mode b15 channel 1 01 channel 2 2 3 b14 b13 b12 b11 b10 b9 b8 b7 b6 b14 b6 b14 b6 b14 b6 b14 b6 b14 b6 b14 b6 b14 b6 b5 b13 b5 b13 b5 b13 b5 b13 b5 b13 b5 b13 b5 b13 b5 b4 b12 b4 b12 b4 b12 b4 b12 b4 b12 b4 b12 b4 b12 b4 b3 b11 b3 b11 b3 b11 b3 b11 b3 b11 b3 b11 b3 b11 b3 b2 b10 b2 b10 b2 b10 b2 b10 b2 b10 b2 b10 b2 b10 b2 b1 b9 b1 b9 b1 b9 b1 b9 b1 b9 b1 b9 b1 b9 b1 b0 b8 b0 b8 b0 b8 b0 b8 b0 b8 b0 b8 b0 b8 b0 b7 b15 b15 b7 b7 b15 b15 b7 b7 b15 b15 b7 b7 b15 channel 1 channel 2 channel 1 channel 2 channel 1 channel 2 conv_start data_ready sclk_adc adc_dout7 adc_dout6 adc_dout5 adc_dout4 adc_dout3 adc_dout2 adc_dout1 adc_dout0 12357-031 figure 45. ppi, 2-channel data sheet adar7251 rev. 0 | page 27 of 72 b15 channel 1 01 channel 2 2 3 b14 b13 b12 b11 b10 b9 b8 b7 b6 b14 b6 b14 b6 b14 b6 b14 b6 b14 b6 b14 b6 b14 b6 b5 b13 b5 b13 b5 b13 b5 b13 b5 b13 b5 b13 b5 b13 b5 b4 b12 b4 b12 b4 b12 b4 b12 b4 b12 b4 b12 b4 b12 b4 b3 b11 b3 b11 b3 b11 b3 b11 b3 b11 b3 b11 b3 b11 b3 b2 b10 b2 b10 b2 b10 b2 b10 b2 b10 b2 b10 b2 b10 b2 b1 b9 b1 b9 b1 b9 b1 b9 b1 b9 b1 b9 b1 b9 b1 b0 b8 b0 b8 b0 b8 b0 b8 b0 b8 b0 b8 b0 b8 b0 b7 b15 b15 b7 b7 b15 b15 b7 b7 b15 b15 b7 b7 b15 channel 3 channel 4 channel 1 channel 2 channel 3 channel 4 data_ready sclk_adc adc_dout7 adc_dout6 adc_dout5 adc_dout4 adc_dout3 adc_dout2 adc_dout1 adc_dout0 12357-032 conv_start figure 46. ppi, 4-channel table 15. bit clock rate options for adc ppi nibble wide mode number of channels fs_adc (mhz) sclk_adc (mhz) data output pins 2 1.2 9.6 adc_dout0 through adc_dout3 4 1.2 19.2 2 1.8 14.4 4 1.8 28.8 adc ppi nibble wide mode adc ppi nibble wide mode differs from byte wide mode in that the data is transferred in nibble form (four bits at a time) instead of in byte wide mode (eight bits at a time). in master mode, the adc outputs the bit clock and data. provide the adc port with a conversion start ( conv_start ); this initiates the conversion process. when the adc is ready with the conversion data, it pulls the data_ready pin high to the dsp. the adc then provides the bit clock, sclk_adc. the data is available on the rising edge of the bit clock. the maximum sample rate supported is 3.6 mhz in this mode. the data is available on the adc_dout0 through adc_dout3 pins, one nibble at a time. the 16-bit data is split into four nibbles each, 4 bits wide. the higher nibble is output first, followed by the lower nibble. the bit clock (sclk) rate depends on the sample rate setting. see table 15 for available options. this mode may be useful if the dsp cannot support the 8-bit wide data port. the data rate is twice that of the ppi byte wide mode; however, it saves four pins. daq mode daq mode is designed specifically for fsk radar applications. in this mode, the adc synchronizes with the fsk clock. both serial and ppi modes are supported, but are limited to master mode. the typical connections for the adc serial master mode (see figure 48) and ppi master mode(see figure 44) are valid. in daq serial mode, the sclk_adc is fixed at 38.4 mhz, whereas the clock rate is adjustable in ppi mode. figure 50 shows the typical operation sequence for the daq serial mode with two channels per data line. adc_dout0 to adc_dout3 adc_dout0 to adc_dout3 master adar7251 slave dsp xin xout sclk gpio1 gpio2 conv_start data_ready sclk_adc 12357-033 figure 47. typical connection diagram for ppi nibble wide mode adar7251 data sheet rev. 0 | page 28 of 72 master adar 7251 slave dsp xin oscillator xout gpio1 gpio2 conv_start data_ready 12357-034 sport1 mclkin sclk_adc fs_adc adc_dout0 adc_dout1 figure 48. typical connection diagram for daq serial master mode b15 channel 1 01 channel 2 2 3 15 b14 b13 b12 b11 b10b6 b2 b14b10b6 b6 b14b10b6 b2 b14b10b6 b2 b9 b5 b1 b13 b9 b5 b5 b13 b9 b5 b1 b13 b9 b5 b1 b8 b4 b0 b12 b8 b4 b0 b12 b8 b4 b0 b12 b8 b4 b0 b3 b7 b7 b3 b11 b15 b7 b3 b11 b15 b7 b3 b11 b15 channel 3 channel 4 channel 1 channel 2 channel 3 channel 4 data_ready sclk_adc adc_dout0 adc_dout1 adc_dout2 adc_dout3 12357-035 figure 49. ppi, 4-cha nnel nibble wide mode t conv t wait (min) = 1sclk + ( t data ? t conv ) if t conv < t data t data = [(2 16)] sclk cycles t wait (min) = 1sclk if t conv > t data 12357-036 data_ready cs sclk_adc adc_dout0 adc_dout1 b15 channel 1 b15 b15 b14 b14 b13 b13 b12 b12 channel 3 b15 channel 2 b1 b1 b0 b0 channel 3 figure 50. daq serial master, two channels per pin data sheet adar7251 rev. 0 | page 29 of 72 t conv t wait (min) = 1sclk + ( t data ? t conv ) if t conv < t data t wait (min) = 1sclk if t conv > t data 12357-037 data_ready cs sclk_adc adc_dout7 adc_dout6 adc_dout5 adc_dout4 adc_dout3 adc_dout2 adc_dout1 adc_dout0 b15 channel 1 channel 2 b14 b7 b15 b7 b6 channel 4 b15 b7 b13 b5 b12 b4 b11 b3 b10 b2 b9 b1 b8 b0 b14 b6 b13 b5 b12 b4 b11 b3 b10 b2 b9 b1 b8 b0 b8 b0 b14 b6 b13 b5 b12 b4 b11 b3 b10 b2 b9 b1 t wait = 1 sclk cycle t data = [(2 # of channels)] sclk cycles figure 51. daq ppi master mode the high to low transition on the conv_start signal starts the conversion process. the adc signals set the data_ready signal high. data is available at the next clock cycle. two channels per pin are supported in serial mode, whereas two or four channels are supported in ppi mode. the sclk frequency determines the total time required for the data (t data ). this value is typically 32-bit clock cycles for serial mode and (2 the number of channels) of bit clock cycles in ppi mode. the fastest data rate available is 57.6 mhz in 2-channel, ppi, 16-cycle acquisition mode. the maximum data rate in daq serial mode is 38.4 mhz and is fixed. the frequency of the conv_start signal dictates the sample rate of the adc in daq mode. calculate the sampling frequency in daq mode as f s daq_mode = 1/( t conv + t wait ) where: t data < t conv . t conv is the time required for the conversion. t wa i t is the time required to wait before another conversion start can be initiated. t data is the time the data is available on the adc_doutx pins. table 16 shows the supported modes and typical acquisition times in daq mode. table 16. acquisition times in daq mode acquisition cycles t conv (s) 16 1.2 24 1.8 32 2.4 using multiple adar7251 devices for systems with more than four channels the adar7251 offers flexible serial port for multichannel applications requiring more than four channels. the typical connection diagram is shown in figure 52. sclk_adc fs_adc adc_dout0 slave dsp master spi adar7251 master adar7251 master xin ss xin ss sport1 optional for > 4 channels adc_dout1 sclk_adc fs_adc adc_dout0 adc_dout1 spi_sclk spi_sclk spi_mosi spi_mosi spi_miso spi_miso spi_mosi spi_sclk spi_ss1 spi_ss2 spi_miso 12357-038 oscillator figure 52. connecting multiple adar7251 devices for an 8-channel system multiple adar7251 devices can be configured using a single spi master and clock oscillator to synchronize the plls of both devices. for the system to function, it is recommended to have both the adcs on the same board and within a few inches of each other. both the devices act as master, but only one adar7251 supplies the bit clock and frame sync signal to the dsp port, which is slave. this connection option may save the adar7251 data sheet rev. 0 | page 30 of 72 extra serial port (sport) on the dsp. this works because both plls are synchronized to one master clock and are enabled at the same time using a single spi master. spi writes must be written to both devices simultaneously. for this to work, the spi_ss pin of both devices must be selected at the same time. the spi reads, however, can be performed independently for both devices. spi control port the adar7251 control port uses a 4-wire spi. the spi port sets the internal registers of the device. the spi allows read and write capability of the registers. all the registers are 16 bits wide. the spi control port supports mode 11 (clock polarity = 1 and clock phase = 1), slave only and, therefore, requires the master in the system to operate. the registers cannot be accessed without the master clock to the device. it is recommended to configure the pll first to achieve full speed on the control port. the port is powered by iovddx, and control signals must be within the iovddx limits. the serial control interface also allows the user to control auxiliary functions of the device such as the gpios and the auxiliary adc. table 17 shows the functions of the control port pins in spi mode. table 17. control port pin functions pin no. mnemonic pin function pin type 32 addr15 sets the device address for the spi input 38 spi_miso spi port outputs data from the adar7251 output 39 spi_mosi spi port inputs data to the adar7251 input 40 spi_clk spi clock to the adar7251 input 41 spi_ss spi slave select to the adar7251 input the spi port uses a 4-wire interface, consisting of the spi_ss , spi_clk, spi_ mosi, and spi_miso signals. the spi port is always a slave port. the spi_ss (slave select) selects the device. the spi_clk is the serial clock input for the device, and all data transfers (either spi_mosi or spi_miso) take place with respect to this clock signal. the spi_mosi pin addresses the on-chip registers and transfers data to these registers. the spi_miso pin outputs data from the on-chip registers. the spi_ss goes low at the beginning of a transaction and high at the end of a transaction. the spi_clk signal samples spi_mosi on a low to high spi_clk transition; therefore, the data to be written to the device must be stable during this edge. the data shifts out of the spi_miso on the falling edge of the spi_clk and must be clocked into a receiving device, such as a microcontroller, on the spi_clk rising edge. the spi_mosi signal carries the serial input data to the adar7251 , and the spi_miso signal carries the serial output data from the device. the spi_miso signal remains tristated until a read operation is requested. this allows direct connection to other spi-compatible peripheral spi_miso ports for sharing the same system controller port. all spi transactions have the same basic format shown in table 19. figure 2 shows an spi port timing diagram. all data must be written msb first. device address r/ w the lsb of the first byte of an spi transaction is a r/ w bit. this bit determines whether the communication is a read (logic level 1) or a write (logic level 0). this format is shown in table 18. table 18. spi address and r/ w byte format bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 0 0 0 0 0 0 addr15 r/ w the addr15 pin (pin 32) determines the address of the device. the device reads the status of this pin on power-up and uses the device address. a 47 k typical resistor must be used to set the device address by using a pull-down resistor to ground or a pull-up resistor to the iovddx pins. pin 32 is multifunctional and is also used as a data output in ppi mode. the r/ w bit setting determines if the device is used for an spi write or spi read operation. when the r/ w bit is set to 0, it is used for an spi write operation; when it is set to 1, it is used for an spi read operation. register address the registers address field is 16 bits wide. the registers start at register 0x000. data bytes the register data field is 16 bits wide. crc the adar7251 provides the user with a 16-bit cyclic redundancy check (crc) for spi read and writes to the device, and for data communication error detection. the crc is enabled by default and can be disabled if not required. disable the crc by writing 0x0001 to register 0xfd00. this spi write disables the crc function. with the crc disabled, the spi read and write sequence is conventional. table 19 shows the typical single read/write byte sequence without the crc; this sequence typically requires 40 clock cycles or 5 bytes. the typical 5-byte sequence consists of byte 0 for the device address with the r/ w bit. the next two bytes, byte 1 and byte 2, contain the register address followed by byte 3 and byte 4, which carry the data to or from the register. a sample timing diagram for a single-word spi write operation to a register is shown in figure 53. figure 54 show a single-word spi read. during the read operation, the spi_miso pin goes from being high impedance (high-z) to output at the beginning of byte 3. figure 55 and figure 56 shows the typical sequence for the multiple byte spi read and writes. data sheet adar7251 rev. 0 | page 31 of 72 ?1 0 1 234567891011121314151617181920212223242526272829303132333435363738394041 r/w device address (7 bits) register address byte 1 register address byte2 data byte1 data byte2 spi_clk spi_ss spi_mosi 12357-039 figure 53. spi write to the adar7251 clocking (single-word write mode), no crc ?1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 r/w device address (7 bits) register address byte1 register address byte2 data byte1 data byte2 spi_clk spi_ss spi_mosi 12357-040 data byte from adar7251 data byte from adar7251 spi_miso figure 54. spi read from the adar7251 clocking (single-word read mode), no crc total clock cycles = 24 + 16 (n); n = number of registers data1 16 bits data2 16 bits device address byte register address 16 bits data byte n ? 1 data byte n spi_ss spi_clk spi_mosi 12357-041 figure 55. spi write to the adar7251 (multiple bytes), no crc device address byte register address byte data2 16 bits data1 16 bits data byte n ? 1 data byte n spi_ss spi_clk spi_mosi spi_miso 12357-042 total clock cycles = 24 + 16 (n); n = number of registers figure 56. spi read from the adar7251 (multiple bytes), no crc table 19. single spi write or read format operation byte 0 byte 1 byte 2 byte 3 byte 4 write device address[6:0], r/w = 0 register address[15:8] register address[7:0] data[15:8] data[7:0] read device address[6:0], r/w = 1 register address[15:8] register address[7:0] data[15:8] data[7:0] table 20. single register write with crc device address register address register data crc 1 byte 2 bytes 2 bytes 2 bytes 00 xxxx 1 xxxx 1 xxxx 1 1 x means dont care. adar7251 data sheet rev. 0 | page 32 of 72 if the crc is enabled, the 16-bit crc must be included in the spi write following the register and data bytes. any spi write that does not include valid crc bits is ignored. the spi write with crc included is as follows for single or multiple registers: 1. the crc is calculated based on the data, excluding the device address byte. 2. the crc polynomial used is (x 16 + x 15 + x 12 + x 7 + x 6 + x 4 + x 3 + 1), that is, xc86ch. 3. the two calculated, 16-bit crc bytes must be appended to the spi writes along with the register address and data bytes for valid transaction. the spi read is limited to 8 bytes (see table 22). three registers must be read one at a time to achieve the crc. the device address is excluded from the eight bytes. the last two bytes represent the crc bytes after the eight bytes (two bytes of the register address + six bytes of the register data). if during the spi write the invalid crc is included, the expected crc value of the last spi transaction is stored in register 0x084 and register 0x085. register 0x084 stores the lower byte, and register 0x085 stores the higher byte. the lower and upper bytes combined form the 16-bit crc value expected in the spi write sequence. register 0x086 enables the crc calculation for the whole register map. it is enabled by default. register 0x087 stores the flag that indicates the crc calculation status. a value of 1 indicates that the crc calculation is ready. in addition, the crc value for the whole register map is stored in register 0x088 and register 0x089. register 0x088 stores the lower byte, whereas register 0x089 stores the higher byte. register 0x084, register 0x085, register 0x087, register 0x 088, and register 0x089 are read only. figure 57 and figure 58 show the spi read and write operations with the crc. table 21. multiple register write with crc device address register address register data register data register data crc 1 byte 2 bytes 2 bytes 2 bytes 2 bytes 2 bytes 00 xxxx 1 xxxx 1 xxxx 1 xxxx 1 xxxx 1 1 x means dont care. table 22. register read with crc device address register address register data register data register data crc 1 byte 2 bytes 2 bytes 2 bytes 2 bytes 2 bytes 01 xxxx 1 xxxx 1 xxxx 1 xxxx 1 xxxx 1 1 x means dont care. ? 101234567891011121314 15161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960 r/w device address (7 bits) register address byte1 register address byte2 data byte1 data byte2 crc lower byte crc uppper byte spi_clk spi_ss spi_mosi 12357-043 figure 57. spi single write with crc r/w device address (7 bits) register address byte1 (8 clock cycles) register address byte2 (8 clock cycles) data byte1 data byte6 crc lower byte crc uppper byte spi_clk spi_ss spi_mosi copy of spi_mosi 12357-044 8 clock cycles 48 clock cycles 8 clock cycles figure 58. spi read with crc data sheet adar7251 rev. 0 | page 33 of 72 pcb layout guidelines the printed circuit board (pcb) layout is an important consideration, as is the component placement of the decoupling capacitors. figure 59 shows the component placement for some of the decoupling capacitors. the decoupling components for avddx, dvddx, iovddx, cm, biasp, biasn, regout_ digital, and pllfilt must be placed close to the device. the 1 nf and 100 nf mlccs must be placed close to their respective pins and on the same layer as the device. the bulk 10 f capacitor can be placed further from the pins. the exposed pad underneath the device must be soldered to the ground plane on the pcb with thermal vias. the recommended footprint for the thermal pad is available at http://www.analog.com/en/content/package- information/fca.html . the typical recommended board stackup is four layers with the top and bottom layers used for signaling, the second layer as the ground plane, and the third layer as the power plane. ensure that the ground plane is contiguous without breaks for the best emi and thermal performance. during the board layout, use the sclk_adc and adc_doutx signals as a transmission line to maintain the signal integrity. 12357-046 avddx ground 1nf 100nf 10f iovddx gnd iovddx dvddx 100nf cm 1nf 100nf pll loop filter xtal avddx 1nf 100nf 1nf 100nf 10f biasn 470nf biasp 470nf regout_digital 100nf pllvdd 10f 10f avddx dvddx iovddx 10f cm 10f 1nf 100nf avddx 100nf figure 59. recommended pcb layout adar7251 data sheet rev. 0 | page 34 of 72 register summary table 23. register summary reg name bits bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 reset rw 0x000 clk_ctrl [15:8] reserved[15:8] 0x0001 rw [7:0] reserved[7:0] pll_bypass 0x001 pll_den [15:8] pll_den[15:8] 0x0000 rw [7:0] pll_den[7:0] 0x002 pll_num [15:8] pll_num[15:8] 0x0000 rw [7:0] pll_num[7:0] 0x003 pll_ctrl [15:8] pll_integer_div reserved[2:0] 0x0000 rw [7:0] pll_input_prescale reserved reserved pll_type pll_en 0x005 pll_lock [15:8] reserved[15:8] 0x0000 r [7:0] reserved[7:0] pll_lock 0x040 master_ enable [15:8] reserved[14:7] 0x0000 rw [7:0] reserved[6:0] master_en 0x041 adc_enable [15:8] reserved 0x00ff rw [7:0] ln_pg4_en ln_pg3_en ln_pg2_en ln_pg1_en adc4_en adc3_en adc2_en adc1_en 0x042 power_ enable [15:8] reserved clock_ loss_en reserved 0x03ff rw [7:0] flash_ ldo_en ldo_en auxadc_en mp_en din_en pout_en sout_en clkgen_en 0x080 asil_clear [15:8] reserved[14:7] 0x0000 rw [7:0] reserved[6:0] asil_clear 0x081 asil_mask [15:8] reserved[9:2] 0x0000 rw [7:0] reserved[1:0] clk_loss_ mask brn_good_ mask brp_good_ mask vr_good_mask overtemp_ mask crc_mask 0x082 asil_flag [15:8] reserved[14:7] 0x0000 r [7:0] reserved[6:0] asil_flag 0x083 asil_error [15:8] reserved[9:2] 0x0000 r [7:0] reserved[1:0] clk_loss_ error brn_error brp_error vr_good_ error overtemp_ error crc_error 0x084 crc_value_l [15:8] reserved[7:0] 0x0000 r [7:0] crc_value_l 0x085 crc_value_h [15:8] reserved[7:0] 0x0000 r [7:0] crc_value_h 0x086 rm_crc_ enable [15:8] reserved[14:7] 0x0000 rw [7:0] reserved[6:0] rm_crc_ enable 0x087 rm_crc_done [15:8] reserved[14:7] 0x0000 r [7:0] reserved[6:0] rm_crc_done 0x088 rm_crc_ value_l [15:8] reserved[7:0] 0x0000 r [7:0] rm_crc_value_l 0x089 rm_crc_ value_h [15:8] reserved[7:0] 0x0000 r [7:0] rm_crc_value_h 0x100 lna_gain [15:8] reserved 0x0000 rw [7:0] lna4_gain lna3_gain lna2_gain lna1_gain 0x101 pga_gain [15:8] reserved 0x0000 rw [7:0] pga4_gain pga3_gain pga2_gain pga1_gain 0x102 adc_ routing1_4 [15:8] reserved adc4_src reserved adc3_src 0x2222 rw [7:0] reserved adc2_src reserved adc1_src 0x140 decim_rate [15:8] reserved[12:5] 0x0003 rw [7:0] reserved[4:0] decim_rate 0x141 high_pass [15:8] reserved[8:1] 0x0018 rw [7:0] reserved [0] phase_eq hp_shift enable_hp data sheet adar7251 rev. 0 | page 35 of 72 reg name bits bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 reset rw 0x143 ack_mode [15:8] reserved[9:2] 0x0000 rw [7:0] reserved[1:0] ack_cycles ack_out_rate ack_mode 0x144 truncate_ mode [15:8] reserved[13:6] 0x0002 rw [7:0] reserved[5:0] trunc_mode 0x1c0 serial_mode [15:8] reserved 0x0000 rw [7:0] reserved clk_src lrclk_ mode lrclk_pol bclk_pol data_fmt tdm_mode 0x1c1 parallel_ mode [15:8] reserved[12:5] 0x0000 rw [7:0] reserved[4:0] par_nibble par_endian par_ channels 0x1c2 output_mode [15:8] reserved[13:6] 0x0000 rw [7:0] reserved[5:0] cs_override output_mode 0x200 adc_read0 [15:8] reserved[5:0] adc_value[9:8] 0x0000 r [7:0] adc_value[7:0] 0x201 adc_read1 [15:8] reserved[5:0] adc_value[9:8] 0x0000 r [7:0] adc_value[7:0] 0x210 adc_speed [15:8] reserved[13:6] 0x0000 rw [7:0] reserved[5:0] adc_speed 0x211 adc_mode [15:8] reserved[12:5] 0x0000 rw [7:0] reserved[4:0] aux_input_sel aux_adc_ mode 0x250 mp0_mode [15:8] reserved[8:1] 0x0000 rw [7:0] reserved[0] debounce_value mp_mode 0x251 mp1_mode [15:8] reserved[8:1] 0x0000 rw [7:0] reserved[0] debounce_value mp_mode 0x260 mp0_write [15:8] reserved[14:7] 0x0000 rw [7:0] reserved[6:0] mp_reg_write 0x261 mp1_write [15:8] reserved[14:7] 0x0000 rw [7:0] reserved[6:0] mp_reg_write 0x270 mp0_read [15:8] reserved[14:7] 0x0000 r [7:0] reserved[6:0] mp_reg_read 0x271 mp1_read [15:8] reserved[14:7] 0x0000 r [7:0] reserved[6:0] mp_reg_read 0x280 spi_clk_pin [15:8] reserved[12:5] 0x0000 rw [7:0] reserved[4:0] spi_clk_pull spi_clk_drive 0x281 miso_pin [15:8] reserved[12:5] 0x0000 rw [7:0] reserved[4:0] miso_pull miso_drive 0x282 ss_pin [15:8] reserved[12:5] 0x0004 rw [7:0] reserved[4:0] ss_pull ss_drive 0x283 mosi_pin [15:8] reserved[12:5] 0x0000 rw [7:0] reserved[4:0] mosi_pull mosi_drive 0x284 addr15_pin [15:8] reserved[12:5] 0x0000 rw [7:0] reserved[4:0] addr15_pull addr15_drive 0x285 fault_pin [15:8] reserved[12:5] 0x0004 rw [7:0] reserved[4:0] fault_pull fault_drive 0x286 fs_adc_pin [15:8] reserved[12:5] 0x0000 rw [7:0] reserved[4:0] fs_adc_pull fs_adc_drive 0x287 cs_pin [15:8] reserved[12:5] 0x0004 rw [7:0] reserved[4:0] cs_pull cs_drive 0x288 sclk_adc_pin [15:8] reserved[12:5] 0x0000 rw [7:0] reserved[4:0] sclk_adc_pull sclk_adc_drive 0x289 adc_dout0_ pin [15:8] reserved[12:5] 0x0000 rw [7:0] reserved[4:0] adc_dout_ pull adc_dout_drive adar7251 data sheet rev. 0 | page 36 of 72 reg name bits bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 reset rw 0x28a adc_dout1_ pin [15:8] reserved[12:5] 0x0000 rw [7:0] reserved[4:0] adc_dout_ pull adc_dout_drive 0x28b adc_dout2_ pin [15:8] reserved[12:5] 0x0000 rw [7:0] reserved[4:0] adc_dout_ pull adc_dout_drive 0x28c adc_dout3_ pin [15:8] reserved[12:5] 0x0000 rw [7:0] reserved[4:0] adc_dout_ pull adc_dout_drive 0x28d adc_dout4_ pin [15:8] reserved[12:5] 0x0000 rw [7:0] reserved[4:0] adc_dout_ pull adc_dout_drive 0x28e adc_dout5_ pin [15:8] reserved[12:5] 0x0000 rw [7:0] reserved[4:0] adc_dout_ pull adc_dout_drive 0x291 data_ready_ pin [15:8] reserved[12:5] 0x0000 rw [7:0] reserved[4:0] data_ready_ pull data_ready_drive 0x292 xtal_ctrl [15:8] reserved[13:6] 0x0000 rw [7:0] reserved[5:0] xtal_drv xtal_enb 0x301 adc_setting1 [15:8] reserved[15:10] eq_cap_ctrl 0x0304 rw [7:0] reserved[7:3] pdetect_en perfom_ improve1 reserved 0x308 adc_setting2 [15:8] reserved[8:1] 0x0000 rw [7:0] reserved[0] perform_improve2 0x30a adc_setting3 [15:8] reserved[11:4] 0x0009 rw [7:0] reserved[3:0] perform_improve5 reserved perform_ improve4 0x30e dejitter_ window [15:8] reserved[15:8] 0x0003 rw [7:0] reserved[7:4] dejitter 0xfd00 crc_en [15:8] reserved[14:7] 0x0000 rw [7:0] reserved[6:0] crc_en data sheet adar7251 rev. 0 | page 37 of 72 register details clock control register address: 0x000, reset: 0x0001, name: clk_ctrl table 24. bit descriptions for clk_ctrl bits bit name settings description reset access 0 pll_bypass use pll or external pin clock. 0x1 rw 1 bypass pll. 0 use pll clock. pll denominator register address: 0x001, reset: 0x0000, name: pll_den table 25. bit descriptions for pll_den bits bit name settings description reset access [15:0] pll_den 0x0001 to 0xffff 16-bit denominator for the pll fractional part range from 0x0001 through 0xffff. denominator value 1 to 65,535. 0x0 rw pll numerator register address: 0x002, reset: 0x0000, name: pll_num table 26. bit descriptions for pll_num bits bit name settings description reset access [15:0] pll_num 0x0001 to 0xffff 16-bit numerator for the pll fractional part range from 0x0001 through 0xffff. numerator value 1 to 65,535. 0x0 rw adar7251 data sheet rev. 0 | page 38 of 72 pll control register address: 0x003, reset: 0x0000, name: pll_ctrl table 27. bit descriptions for pll_ctrl bits bit name settings description reset access [15:11] pll_integer_div integer part of the pll multiplier. 0x00 rw 0x1 to 0x1f multiplier 1 to 31. [7:4] pll_input_prescale pll input prescaler. 0x0 rw 0x0 to 0xf prescale value from 1 through 16. 1 pll_type type of pll. 0x0 rw 0 pll is in integer mode. 1 pll is in fractional mode. 0 pll_en pll enable. 0x0 rw 0 pll is disabled. 1 pll is enabled. pll status register address: 0x005, reset: 0x0000, name: pll_lock table 28. bit descriptions for pll_lock bits bit name settings description reset access 0 pll_lock pll lock bit. 0x0 r 0 pll is unlocked. 1 pll is locked. data sheet adar7251 rev. 0 | page 39 of 72 master enable switch register address: 0x040, reset: 0x0000, name: master_enable table 29. bit descriptions for master_enable bits bit name settings description reset access 0 master_en master enable switch. 0x0 rw 0 disables the entire chip. 1 enables the entire chip. adc enable register address: 0x041, reset: 0x00ff, name: adc_enable table 30. bit descriptions for adc_enable bits bit name settings description reset access 7 ln_pg4_en lna and pga enable channel 4. 0x1 rw 0 disable the lna/pga channel 4. 1 enable the lna/pga channel 4. 6 ln_pg3_en lna and pga enable channel 3. 0x1 rw 0 disable the lna/pga channel 3. 1 enable the lna/pga channel 3. adar7251 data sheet rev. 0 | page 40 of 72 bits bit name settings description reset access 5 ln_pg2_en lna and pga enable channel 2. 0x1 rw 0 disable the lna/pga channel 2. 1 enable the lna/pga channel 2. 4 ln_pg1_en lna and pga enable channel 1. 0x1 rw 0 disable the lna/pga channel 1. 1 enable the lna/pga channel 1. 3 adc4_en adc 4 enable. 0x1 rw 0 disable adc 4. 1 enable adc 4. 2 adc3_en adc 3 enable. 0x1 rw 0 disable adc 3. 1 enable adc 3. 1 adc2_en adc 2 enable. 0x1 rw 0 disable adc 2. 1 enable adc 2. 0 adc1_en adc 1 enable. 0x1 rw 0 disable adc 1. 1 enable adc 1. power enable register address: 0x042, reset: 0x03ff, name: power_enable table 31. bit descriptions for power_enable bits bit name settings description reset access 9 clock_loss_en enables clock loss. 0x1 rw 0 disables clock loss detect. 1 enables clock loss detect. 7 flash_ldo_en flash ldo block enable. 0x1 rw data sheet adar7251 rev. 0 | page 41 of 72 bits bit name settings description reset access 6 ldo_en ldo block enable. 0x1 rw 0 ldo disable. 1 ldo enable. 5 auxadc_en aux adc block enable. 0x1 rw 0 disable adc power. 1 enable adc power. 4 mp_en multipurpose pin enable. 0x1 rw 0 gpio pin disable. 1 gpio pin enable. 3 din_en serial input block enable. 0x1 rw 0 disable serial input port. 1 enable serial input port. 2 pout_en parallel outp ut block enable. 0x1 rw 0 disable parallel output port. 1 enable parallel output port. 1 sout_en serial output block enable. 0x1 rw 0 disable serial output port. 1 enable serial output port. 0 clkgen_en clock generator block enable. 0x1 rw 0 disable clock generator. 1 enable clock generator. clear the asil errors register address: 0x080, reset: 0x0000, name: asil_clear table 32. bit descriptions for asil_clear bits bit name settings description reset access 0 asil_clear clear the automotive safety integrity level (asil) errors. 0x0 rw 0 asil errors are reported. 1 clears the asil error. set back to 0 after reading the asil register. if left at 1, no asil errors are reported. adar7251 data sheet rev. 0 | page 42 of 72 selects which errors to mask register address: 0x081, reset: 0x0000, name: asil_mask table 33. bit descriptions for asil_mask bits bit name settings description reset access 5 clk_loss_mask clock loss error mask. 0x0 rw 0 clock loss error not masked. 1 clock loss error masked. 4 brn_good_mask biasn voltage error mask. 0x0 rw 0 biasn voltage error not masked. 1 biasn voltage error masked. 3 brp_good_mask biasp voltage error mask. 0x0 rw 0 biasp voltage error not masked. 1 biasp voltage error masked. 2 vr_good_mask reference voltage error mask. 0x0 rw 0 reference voltage error not masked. 1 reference voltage error masked. 1 overtemp_mask overtemperature error mask. 0x0 rw 0 overtemperature flag not masked. 1 overtemperature flag masked. 0 crc_mask crc error mask. 0x0 rw 0 crc error not masked. 1 crc error masked. data sheet adar7251 rev. 0 | page 43 of 72 asil error flag register address: 0x082, reset: 0x0000, name: asil_flag table 34. bit descriptions for asil_flag bits bit name settings description reset access 0 asil_flag indicates an asil error. 0x0 r 0 no error. 1 asil error. asil error code register address: 0x083, reset: 0x0000, name: asil_error table 35. bit descriptions for asil_error bits bit name settings description reset access 5 clk_loss_error clock loss error. 0x0 r 0 clock available. 1 clock loss error. 4 brn_error biasn error. 0x0 r 0 biasn ok. 1 biasn error. 3 brp_error biasp error. 0x0 r 0 biasp ok. 1 biasp error. 2 vr_good_error voltage reference error. 0x0 r 0 voltage reference ok. 1 voltage reference error. adar7251 data sheet rev. 0 | page 44 of 72 bits bit name settings description reset access 1 overtemp_error overtemperature error. 0x0 r 0 normal. 1 overtemperature error. 0 crc_error crc error. 0x0 r 0 no crc error. 1 crc error. crc value, bits[7:0] register address: 0x084, reset: 0x0000, name: crc_value_l table 36. bit descriptions for crc_value_l bits bit name settings description reset access [7:0] crc_value_l crc value lower byte. 0x0 r 0x00 to 0xff crc value lower byte. crc value register address: 0x085, reset: 0x0000, name: crc_value_h table 37. bit descriptions for crc_value_h bits bit name settings description reset access [7:0] crc_value_h crc value upper byte. 0x0 r 0x00 to 0xff crc value upper byte. data sheet adar7251 rev. 0 | page 45 of 72 start calculating the crc value of the register map content register address: 0x086, reset: 0x0000, name: rm_crc_enable table 38. bit descriptions for rm_crc_enable bits bit name settings description reset access 0 rm_crc_enable crc enable. 0x0 rw 0 crc enable. 1 crc disable. register map crc calculation done register address: 0x087, reset: 0x0000, name: rm_crc_done table 39. bit descriptions for rm_crc_done bits bit name settings description reset access 0 rm_crc_done register map crc calculation done. 0x0 r 0 crc calculation not done. 1 crc calculation done. register map crc value, bits[7:0] register address: 0x088, reset: 0x0000, name: rm_crc_value_l table 40. bit descriptions for rm_crc_value_l bits bit name settings description reset access [7:0] rm_crc_value_l 0x0000 to 0xffff regmap crc lower byte. 0x0 r adar7251 data sheet rev. 0 | page 46 of 72 register map crc value, bits[15:8] register address: 0x089, reset: 0x0000, name: rm_crc_value_h table 41. bit descriptions for rm_crc_value_h bits bit name settings description reset access [7:0] rm_crc_value_h regmap crc value upper byte. 0x0 r 0x0000 to 0xffff regmap crc value upper byte. low noise amplifier gain control register address: 0x100, reset: 0x0000, name: lna_gain table 42. bit descriptions for lna_gain bits bit name settings description reset access [7:6] lna4_gain lna gain for channel 4. 0x0 rw 00 gain of 2. 01 gain of 4. 10 gain of 8. 11 gain of 16. [5:4] lna3_gain lna gain for channel 3. 0x0 rw 00 gain of 2. 01 gain of 4. 10 gain of 8. 11 gain of 16. data sheet adar7251 rev. 0 | page 47 of 72 bits bit name settings description reset access [3:2] lna2_gain lna gain for channel 2. 0x0 rw 00 gain of 2. 01 gain of 4. 10 gain of 8. 11 gain of 16. [1:0] lna1_gain lna gain for channel 1. 0x0 rw 00 gain of 2. 01 gain of 4. 10 gain of 8. 11 gain of 16. programmable gain amplifier gain control register address: 0x101, reset: 0x0000, name: pga_gain table 43. bit descriptions for pga_gain bits bit name settings description reset access [7:6] pga4_gain pga gain for channel 4. 0x0 rw 00 gain of 1.4. 01 gain of 2.8. 10 gain of 5.6. 11 gain of 11.2. [5:4] pga3_gain pga gain for channel 3. 0x0 rw 00 gain of 1.4. 01 gain of 2.8. 10 gain of 5.6. 11 gain of 11.2. [3:2] pga2_gain pga gain for channel 2. 0x0 rw 00 gain of 1.4. 01 gain of 2.8. 10 gain of 5.6. 11 gain of 11.2. adar7251 data sheet rev. 0 | page 48 of 72 bits bit name settings description reset access [1:0] pga1_gain pga gain for channel 1. 0x0 rw 00 gain of 1.4. 01 gain of 2.8. 10 gain of 5.6. 11 gain of 11.2. signal path for adc 1 through adc 4 register address: 0x102, reset: 0x2222, name: adc_routing1_4 table 44. bit descriptions for adc_routing1_4 bits bit name settings description reset access [14:12] adc4_src signal source for adc4. 0x2 rw 000 adc disabled. 001 lna pga eq path. 010 lna pga path (bypass eq). 011 bypass lna, pga, and eq. 100 swap channels. 101 use test pin. [10:8] adc3_src signal source for adc3. 0x2 rw 000 adc disabled. 001 lna pga eq path. 010 lna pga path (bypass eq). 011 bypass lna, pga, and eq. 100 swap channels. 101 use test pin. data sheet adar7251 rev. 0 | page 49 of 72 bits bit name settings description reset access [6:4] adc2_src signal source for adc2. 0x2 rw 000 adc disabled. 001 lna pga eq path. 010 lna pga path (bypass eq). 011 bypass lna, pga, and eq. 100 swap channels. 101 use test pin. [2:0] adc1_src signal source for adc1. 0x2 rw 000 adc disabled. 001 lna pga eq path. 010 lna pga path (bypass eq). 011 bypass lna, pga, and eq. 100 swap channels. 101 use test pin. decimator rate control register address: 0x140, reset: 0x0003, name: decim_rate table 45. bit descriptions for decim_rate bits bit name settings description reset access [2:0] decim_rate decimator rate. 0x3 rw 000 reserved. 001 reserved. 010 1.8 msps. 011 1.2 msps. 100 900 ksps. 101 600 ksps. 110 450 ksps. 111 300 ksps. adar7251 data sheet rev. 0 | page 50 of 72 high pass filter control register address: 0x141, reset: 0x0018, name: high_pass table 46. bit descriptions for high_pass bits bit name settings description reset access 6 phase_eq enable the 4 th -order eq. 0x0 rw 0 phase eq is off. 1 phase eq is on. [5:1] hp_shift shift value for high-pass filter. 0x0c rw 00000 dc cal mode. 01011 hp shift value 11. 01100 hp shift value 12. 01101 hp shift value 13. 01110 hp shift value 14. 01111 hp shift value 15. 10000 hp shift value 16. 10001 hp shift value 17. 10010 hp shift value 18. 0 enable_hp enables the high-pass filter. 0x0 rw 0 hp filter is off. 1 hp filter is on. data sheet adar7251 rev. 0 | page 51 of 72 daq mode control register address: 0x143, reset: 0x0000, name: ack_mode table 47. bit descriptions for ack_mode bits bit name settings description reset access [5:4] ack_cycles selects the number of acquisition cycles in daq mode. 0x0 rw 00 16-cycle acquisition. 01 24-cycle acquisition. 10 32-cycle acquisition. 11 reserved. [3:1] ack_out_rate selects the data output rate in daq mode. 0x0 rw 000 57.6 mhz. 001 38.4 mhz. 010 28.8 mhz. 011 19.2 mhz. 100 14.4 mhz. 101 9.6 mhz. 110 7.2 mhz. 111 4.8 mhz. 0 ack_mode selects the data conversion mode. 0x0 rw 0 default continuous mode. 1 daq mode. adar7251 data sheet rev. 0 | page 52 of 72 decimator truncate control register address: 0x144, reset: 0x0002, name: truncate_mode table 48. bit descriptions for truncate_mode bits bit name settings description reset access [1:0] trunc_mode decimator word truncation method. 0x2 rw 00 truncate lsbs. 01 round to zero. 10 normal rounding. 11 reserved. serial output port control register address: 0x1c0, reset: 0x0000, name: serial_mode table 49. bit descriptions for serial_mode bits bit name settings description reset access 6 clk_src sclk_adc source. 0x0 rw 0 slave. 1 master. 5 lrclk_mode frame sync (fs_adc) mode. 0x0 rw 0 50/50 duty cycle clock. 1 pulse. data sheet adar7251 rev. 0 | page 53 of 72 bits bit name settings description reset access 4 lrclk_pol frame sync (fs_adc) polarity. 0x0 rw 0 negative polarity. 1 positive polarity. 3 bclk_pol sclk_adc polarity. 0x0 rw 0 negative polarity. 1 positive polarity. 2 data_fmt serial data format. 0x0 rw 0 left justified format. 1 i2s formatdata delayed by 1 sclk period. [1:0] tdm_mode channels per frame and sclk cycles per channel. 0x0 rw 00 2 channels, 16 bits per channel. 01 4 channels, 16 bits per channel. 10 reserved. 11 reserved. parallel port control register address: 0x1c1, reset: 0x0000, name: parallel_mode table 50. bit descriptions for parallel_mode bits bit name settings description reset access 2 par_nibble enable nibble mode. 0x0 rw 1 byte mode. 0 nibble mode. 1 par_endian high byte/low byte order. 0x0 rw 0 high byte goes out first. 1 low byte goes out first. 0 par_channels number of channels to be output. 0x0 rw 1 2 channels. 0 4 channels. adar7251 data sheet rev. 0 | page 54 of 72 adc digital output mode register address: 0x1c2, reset: 0x0000, name: output_mode table 51. bit descriptions for output_mode bits bit name settings description reset access 1 cs_override conv_start enable or disable. 0x0 rw 0 conv_start function is enabled 1 conv_start function is disabled 0 output_mode serial or parallel mode. 0x0 rw 0 serial mode 1 parallel mode auxiliary adc read value registers address: 0x200, reset: 0x0000, name: adc_read0 this register contains the output data of the auxiliary adc for the given channel. each of the two channels are updated once pe r sample frame. table 52. bit descriptions for adc_read0 bits bit name settings description reset access [9:0] adc_value adc input value. instantaneous value of the sampled data on the adc input. 0x000 rw data sheet adar7251 rev. 0 | page 55 of 72 address: 0x201, reset: 0x0000, name: adc_read1 this register contains the output data of the auxiliary adc for the given channel. each of the two channels are updated once pe r sample frame. table 53. bit descriptions for adc_read1 bits bit name settings description reset access [9:0] adc_value adc input value. instantaneous value of the sampled data on the adc input. 0x000 rw auxiliary adc sample rate selection register address: 0x210, reset: 0x0000, name: adc_speed this register sets the sample rate for the auxiliary adcs. table 54. bit descriptions for adc_speed bits bit name settings description reset access [1:0] adc_speed adc speed. test register allowing the auxiliary adcs to be sampled at double rate or half rate. 0x0 rw 00 112.5 khz sample rate. 01 225 khz sample rate. 10 450 khz sample rate. 11 reserved. adar7251 data sheet rev. 0 | page 56 of 72 auxiliary adc mode register address: 0x211, reset: 0x0000, name: adc_mode table 55. bit descriptions for adc_mode bits bit name settings description reset access [2:1] aux_input_sel aux input selection. 0x0 rw 00 auxin1 pin used for adc 01 auxin2 pin used for adc 0 aux_adc_mode aux adc mode. 0x0 rw 0 both pins are sampled once every sample period. 1 only one pin is sampled twice every sample period. the pin is selected based on aux_input_sel bits[2:1]. mpx pin modes registers address: 0x250, reset: 0x0000, name: mp0_mode table 56. bit descriptions for mp0_mode bits bit name settings description reset access [5:2] debounce_value debounce time setting. 0x0 rw 0001 0.3 ms debounce. 0010 0.6 ms debounce. 0011 0.9 ms debounce. 0100 5.0 ms debounce. 0101 10.0 ms debounce. 0110 20.0 ms debounce. data sheet adar7251 rev. 0 | page 57 of 72 bits bit name settings description reset access 0111 40.0 ms debounce. 0000 no debounce. [1:0] mp_mode mode setting for mp. 0x0 rw 01 pin used as an input. 10 pin used as an output. 00 primary function of the pin is selected. address: 0x251, reset: 0x0000, name: mp1_mode table 57. bit descriptions for mp1_mode bits bit name settings description reset access [5:2] debounce_value debounce time setting. 0x0 rw 0001 0.3 ms debounce. 0010 0.6 ms debounce. 0011 0.9 ms debounce. 0100 5.0 ms debounce. 0101 10.0 ms debounce. 0110 20.0 ms debounce. 0111 40.0 ms debounce. 0000 no debounce. [1:0] mp_mode mode setting for mp. 0x0 rw 01 pin used as an input. 10 pin used as an output. 00 primary function of the pin is selected. adar7251 data sheet rev. 0 | page 58 of 72 mp write value registers address: 0x260, reset: 0x0000, name: mp0_write table 58. bit descriptions for mp0_write bits bit name settings description reset access 0 mp_reg_write multipurpose pin write value. 0x0 w 0 mp pin output off. 1 mp pin output on. address: 0x261, reset: 0x0000, name: mp1_write table 59. bit descriptions for mp1_write bits bit name settings description reset access 0 mp_reg_write multipurpose pin write value. 0x0 w 0 mp pin output off. 1 mp pin output on. mp read value registers address: 0x270, reset: 0x0000, name: mp0_read table 60. bit descriptions for mp0_read bits bit name settings description reset access 0 mp_reg_read multipurpose pin read value. 0x0 r 0 mp pin input low. 1 mp pin input high. data sheet adar7251 rev. 0 | page 59 of 72 address: 0x271, reset: 0x0000, name: mp1_read table 61. bit descriptions for mp1_read bits bit name settings description reset access 0 mp_reg_read multipurpose pin read value. 0x0 r 0 mp pin input low. 1 mp pin input high. spi_clk pin drive strength and slew rate register address: 0x280, reset: 0x0000, name: spi_clk_pin table 62. bit descriptions for spi_clk_pin bits bit name settings description reset access 2 spi_clk_pull spi_clk pull-down. 0x0 rw 0 pull-down disabled. 1 pull-down enabled. [1:0] spi_clk_drive spi_clk drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. adar7251 data sheet rev. 0 | page 60 of 72 spi_miso pin drive strength and slew rate register address: 0x281, reset: 0x0000, name: miso_pin table 63. bit descriptions for miso_pin bits bit name settings description reset access 2 miso_pull spi_miso pull-down. 0x0 rw 0 pull-down disabled. 1 pull-down enabled. [1:0] miso_drive spi_miso drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. spi_ss pin drive strength and slew rate register address: 0x282, reset: 0x0004, name: ss_pin table 64. bit descriptions for ss_pin bits bit name settings description reset access 2 ss_pull spi_ss pull-up. 0x1 rw 0 pull-up disabled. 1 pull-up enabled. data sheet adar7251 rev. 0 | page 61 of 72 bits bit name settings description reset access [1:0] ss_drive spi_ss drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. spi_mosi pin drive strength and slew rate register address: 0x283, reset: 0x0000, name: mosi_pin table 65. bit descriptions for mosi_pin bits bit name settings description reset access 2 mosi_pull spi_mosi pull-down. 0x0 rw 0 pull-down disabled. 1 pull-down enabled. [1:0] mosi_drive spi_mosi drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. adar7251 data sheet rev. 0 | page 62 of 72 addr15 pin drive strength and slew rate register address: 0x284, reset: 0x0000, name: addr15_pin this register also controls the drive strength setting for adc_dout6 in ppi mode. table 66. bit descriptions for addr15_pin bits bit name settings description reset access 2 addr15_pull addr15 pull-down. 0x0 rw 0 pull-down disabled. 1 pull-down enabled. [1:0] addr15_drive addr15 drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. fault pin drive strength and slew rate register address: 0x285, reset: 0x0004, name: fault_pin table 67. bit descriptions for fault_pin bits bit name settings description reset access 2 fault_pull fault pull-up. 0x1 rw 0 pull-up disabled. 1 pull-up enabled. data sheet adar7251 rev. 0 | page 63 of 72 bits bit name settings description reset access [1:0] fault_drive fault drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. fs_adc pin drive strength and slew rate register address: 0x286, reset: 0x0000, name: fs_adc_pin this register also controls the drive strength setting for adc_dout7 in ppi mode. table 68. bit descriptions for fs_adc_pin bits bit name settings description reset access 2 fs_adc_pull fs_adc pull-down. 0x0 rw 0 pull-down disabled. 1 pull-down enabled. [1:0] fs_adc_drive fs_adc drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. adar7251 data sheet rev. 0 | page 64 of 72 conv_start pin drive strength and slew rate register address: 0x287, reset: 0x0004, name: cs_pin table 69. bit descriptions for cs_pin bits bit name settings description reset access 2 cs_pull conv_start pull-up. 0x1 rw 0 pull-up disabled. 1 pull-up enabled. [1:0] cs_drive conv_start drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. sclk_adc pin drive strength and slew rate register address: 0x288, reset: 0x0000, name: sclk_adc_pin table 70. bit descriptions for sclk_adc_pin bits bit name settings description reset access 2 sclk_adc_pull sclk_adc pull-down. 0x0 rw 0 pull-down disabled. 1 pull-down enabled. [1:0] sclk_adc_drive sclk_adc drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. data sheet adar7251 rev. 0 | page 65 of 72 adc_doutx pins drive strength and slew rate registers the following registers refer to the adc_doutx pins. this range includes adc_dout0 through adc_dout5. for bits[1:0] and bit 2 in table 71 through table 76, adc_dout refers to the adc_doutx pin defined by the register name. address: 0x289, reset: 0x0000, name: adc_dout0_pin table 71. bit descriptions for adc_dout0_pin bits bit name settings description reset access 2 adc_dout_pull adc_dout pull-down. 0x0 rw 0 pull-down disabled. 1 pull-down enabled. [1:0] adc_dout_drive adc_dout drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. address: 0x28a, reset: 0x0000, name: adc_dout1_pin table 72. bit descriptions for adc_dout1_pin bits bit name settings description reset access 2 adc_dout_pull adc_dout pull-down. 0x0 rw 0 pull-down disabled. 1 pull-down enabled. [1:0] adc_dout_drive adc_dout drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. adar7251 data sheet rev. 0 | page 66 of 72 address: 0x28b, reset: 0x0000, name: adc_dout2_pin table 73. bit descriptions for adc_dout2_pin bits bit name settings description reset access 2 adc_dout_pull adc_dout pull-down. 0x0 rw 0 pull-down disabled. 1 pull-down enabled. [1:0] adc_dout_drive adc_dout drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. address: 0x28c, reset: 0x0000, name: adc_dout3_pin table 74. bit descriptions for adc_dout3_pin bits bit name settings description reset access 2 adc_dout_pull adc_dout pull-down. 0x0 rw 0 pull-down disabled. 1 pull-down enabled. [1:0] adc_dout_drive adc_dout drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. data sheet adar7251 rev. 0 | page 67 of 72 address: 0x28d, reset: 0x0000, name: adc_dout4_pin table 75. bit descriptions for adc_dout4_pin bits bit name settings description reset access 2 adc_dout_pull adc_dout pull-down. 0x0 rw 0 pull-down disabled. 1 pull-down enabled. [1:0] adc_dout_drive adc_dout drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. address: 0x28e, reset: 0x0000, name: adc_dout5_pin table 76. bit descriptions for adc_dout5_pin bits bit name settings description reset access 2 adc_dout_pull adc_dout pull-down. 0x0 rw 0 pull-down disabled. 1 pull-down enabled. [1:0] adc_dout_drive adc_dout drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. adar7251 data sheet rev. 0 | page 68 of 72 data_ready pin drive strength and slew rate register address: 0x291, reset: 0x0000, name: data_ready_pin table 77. bit descriptions for data_ready_pin bits bit name settings description reset access 2 data_ready_pull data_ready pull-down. 0x0 rw 0 pull-down disabled. 1 pull-down enabled. [1:0] data_ready_drive data_ready drive strength. 0x0 rw 00 lowest. 01 low. 10 high. 11 highest. xtal enable and drive register address: 0x292, reset: 0x0000, name: xtal_ctrl table 78. bit descriptions for xtal_ctrl bits bit name settings description reset access 1 xtal_drv drive strength of xout pin. 0x0 rw 0 low. 1 high. 0 xtal_enb crystal oscillator enable. 0x0 rw 0 xtal enable. 1 xtal disable. data sheet adar7251 rev. 0 | page 69 of 72 adc test register address: 0x301, reset: 0x0304, name: adc_setting1 table 79. bit descriptions for adc_setting1 bits bit name settings description reset access [9:8] eq_cap_ctrl hpf corner frequency select. 0x3 rw 00 eq hpf corner frequency 54 khz 01 eq hpf corner frequency 45 khz 10 eq hpf corner frequency 37 khz 11 eq hpf corner frequency 32 khz 2 pdetect_en peak detect enable. 0x1 rw 0 peak detect disable 1 peak detect enable 1 perfom_improve1 performance improvement setting 1. 0x0 rw 0 performance improvement setting 1 enable 1 performance improvement setting 1 disable (use this value) address: 0x308, reset: 0x0000, name: adc_setting2 table 80. bit descriptions for adc_setting2 bits bit name settings description reset access [4:0] perform_improve2 performance improvement setting 2. 0x00 rw 0xxxx performance improvement setting 2a. 1xxxx performance improvement setting 2b. 10011 performance improvement setting 2c (use this value) adar7251 data sheet rev. 0 | page 70 of 72 address: 0x30a, reset: 0x0009, name: adc_setting3 table 81. bit descriptions for adc_setting3 bits bit name settings description reset access [3:2] perform_improve5 performance improvement setting 5. 0x2 rw 10 reserved. 00 performance improvement setting 5 (use this setting). 0 perform_improve4 performance improvement setting 4. 0x1 rw 0 performance improvement setting 4 disable. 1 performance improvement setting 4 enable (use this setting). digital filter sync enable register address: 0x30e, reset: 0x0003, name: dejitter_window table 82. bit descriptions for dejitter_window bits bit name settings description reset access [3:0] dejitter digital filter sync enable. 0x3 rw 0000 digital filter sync disable. 0011 digital filter sync enable. crc enable/disable register address: 0xfd00, reset: 0x0000, name: crc_en table 83. bit descriptions for crc_en bits bit name settings description reset access 0 crc_en 0x0 rw 0 crc enable 1 crc disable data sheet adar7251 rev. 0 | page 71 of 72 typical application circuit a vdd ain1p avdd1 avdd2 avdd3 pllvdd dvdd1 dvdd2 iovdd1 iovdd2 regout_digital c1 c2 c3 ain1n ain2p c4 c5 c6 from mmic ain2n ain3p adar7251 c7 c8 c9 ain3n ain4p c10 c11 c12 c15 470nf c16 470nf c13 10f c14 100nf y1 r1 r4 r3 r6 r5 c18 c17 c19 r2 c20 ain4n adc_dout0 addr15 auxin1 auxin2 cm biasp biasn iovdd c35 10f c34 100nf c30 100nf c33 10f c31 10f c29 10f c28 100nf c27 10f c24 10f c26 100nf c23 100nf c21 10f c22 100nf c25 100nf c32 100nf avddx adc_dout1 fs_adc fault spi_miso spi_mosi spi_clk spi_ss sclk_adc conv_start data_ready c1, c2, c4, c5, c7, c8, c10, c11: see high-pass filter (hpf) section c3, c6, c9, c12: see low-pass filter (lpf) section c17, c18: 12pf to 18pf, select based on crystal r1: 100 ? typical. select based on crystal c19: 5.6nf c20: 390pf r2: 1k ? ? ; use either pull-up or pull-down based on device address r5, r6: 10k ? typical conv_start and data_ready signals may not be necessary, see adc serial mode section fs_adc and sclk_adc direction depends on the master or slave mode y 1: 19.2mhz typical. acceptable range is 16mhz to 54mhz. alternately clock available in the system can be connected to xin. iovdd microcontroller iovdd xin xout pllfilt agnd1 agnd2 agnd3 pllgnd dgnd1 dgnd2 dgnd3 aux inputs dsp 12357-045 figure 60. typical application circuit, 4-channel, serial mode adar7251 data sheet rev. 0 | page 72 of 72 outline dimensions 01-28-2014-a 1 0.50 bsc bottom view top view pin 1 indicator 48 13 24 25 36 37 12 exposed pad p i n 1 i n d i c a t o r seating plane 0.05 max 0.02 nom 0.203 ref 0.30 min 0.075~0.150 (step dimension) coplanarity 0.08 0.30 0.25 0.20 7.10 7.00 sq 6.90 0.80 0.75 0.70 for proper connection of the exposed pad, refer to the pin configuration and function descriptions section of this data sheet. 0.51 0.45 0.41 5.70 5.60 sq 5.50 5.50 ref pkg-4277 figure 61. 48-lead lead frame chip scale package [lfcsp_ss] 7 mm 7 mm body, with side solderable leads (cs-48-1) dimensions shown in millimeters ordering guide model 1, 2 temperature range package description package option adar7251wbcsz ?40c to +125c 48-lead lfcsp_ss cs-48-1 adar7251wbcsz-rl ?40c to +125c 48-lead lfcsp_ss, 13 tape and reel cs-48-1 eval-adar7251z evaluation board 1 z = rohs compliant part. 2 w = qualified for auto motive applications. automotive products the adar7251w models are available with controlled manufacturing to support the quality and reliability requirements of automot ive applications. note that these automotive models may have specifications that differ from the commercial models; therefore, desi gners should review the specifications section of this data sheet carefully. only the automotive grade products shown are available f or use in automotive applications. contact your local analog devices account representative for specific product ordering information and to obtain the specific automotive reliability reports for these models. ?2014 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. d12357-0-11/14(0) |
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